diff --git a/public/images/blog/react-labs-april-2025/flip.gif b/public/images/blog/react-labs-april-2025/flip.gif
new file mode 100644
index 0000000000..a7363ebf62
Binary files /dev/null and b/public/images/blog/react-labs-april-2025/flip.gif differ
diff --git a/public/images/blog/react-labs-april-2025/perf_tracks.png b/public/images/blog/react-labs-april-2025/perf_tracks.png
new file mode 100644
index 0000000000..835a247cf6
Binary files /dev/null and b/public/images/blog/react-labs-april-2025/perf_tracks.png differ
diff --git a/public/images/blog/react-labs-april-2025/perf_tracks.webp b/public/images/blog/react-labs-april-2025/perf_tracks.webp
new file mode 100644
index 0000000000..88a7eb792b
Binary files /dev/null and b/public/images/blog/react-labs-april-2025/perf_tracks.webp differ
diff --git a/public/images/blog/react-labs-april-2025/perf_tracks_dark.png b/public/images/blog/react-labs-april-2025/perf_tracks_dark.png
new file mode 100644
index 0000000000..07513fe90b
Binary files /dev/null and b/public/images/blog/react-labs-april-2025/perf_tracks_dark.png differ
diff --git a/public/images/blog/react-labs-april-2025/perf_tracks_dark.webp b/public/images/blog/react-labs-april-2025/perf_tracks_dark.webp
new file mode 100644
index 0000000000..1a0521bf89
Binary files /dev/null and b/public/images/blog/react-labs-april-2025/perf_tracks_dark.webp differ
diff --git a/src/components/Icon/IconExperimental.tsx b/src/components/Icon/IconExperimental.tsx
new file mode 100644
index 0000000000..0bba612ebc
--- /dev/null
+++ b/src/components/Icon/IconExperimental.tsx
@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ */
+
+import {memo} from 'react';
+
+export const IconExperimental = memo<
+  JSX.IntrinsicElements['svg'] & {title?: string; size?: 's' | 'md'}
+>(function IconCanary(
+  {className, title, size} = {
+    className: undefined,
+    title: undefined,
+    size: 'md',
+  }
+) {
+  return (
+    <svg
+      className={className}
+      width={size === 's' ? '12px' : '20px'}
+      height={size === 's' ? '12px' : '20px'}
+      viewBox="0 0 20 20"
+      version="1.1"
+      xmlns="http://www.w3.org/2000/svg">
+      {title && <title>{title}</title>}
+      <g stroke="none" strokeWidth="1" fill="none" fillRule="evenodd">
+        <g
+          id="noun-labs-1201738-(2)"
+          transform="translate(2, 0)"
+          fill="currentColor"
+          fillRule="nonzero">
+          <path
+            d="M10.2865804,5.55665262 L10.2865804,2.22331605 L10.8591544,2.22331605 C11.0103911,2.22244799 11.1551447,2.16342155 11.2617505,2.05914367 C11.3684534,1.95486857 11.4282767,1.81370176 11.4282767,1.66667106 L11.4282767,0.556642208 C11.4282767,0.40907262 11.3678934,0.26747526 11.2605218,0.16308627 C11.1531503,0.0587028348 11.0074938,0 10.8556998,0 L5.14338868,0 C4.9915947,0 4.84594391,0.0587028348 4.73856664,0.16308627 C4.63119507,0.267469704 4.57081178,0.40907262 4.57081178,0.556642208 L4.57081178,1.66667106 C4.57081178,1.81434899 4.63119507,1.95594912 4.73856664,2.06033811 C4.8459382,2.16472155 4.9915947,2.22331605 5.14338868,2.22331605 L5.71596273,2.22331605 L5.71596273,5.55665262 C5.71596273,8.38665538 2.97295619,9.88999017 0.651686904,15.5566623 C-0.0957823782,17.360053 -2.00560068,20 7.99951567,20 C18.004632,20 16.0948137,17.3600252 15.3507732,15.5566623 C13.0124432,9.88999017 10.2865804,8.38665538 10.2865804,5.55665262 Z M9.89570197,10.709991 C10.0921412,10.709991 10.2805515,10.7858383 10.4193876,10.9209301 C10.5583466,11.0559135 10.6363652,11.2390693 10.6363652,11.4300417 C10.6363652,11.6210141 10.5583466,11.8040698 10.4193876,11.9391533 C10.2805401,12.0741367 10.0921412,12.1499813 9.89570197,12.1499813 C9.6992627,12.1499813 9.51096673,12.074134 9.37201631,11.9391533 C9.23316875,11.8040615 9.15515307,11.6210141 9.15515307,11.4300417 C9.15515307,11.2390693 9.2331716,11.0559024 9.37201631,10.9209301 C9.57264221,10.7258996 9.61239426,10.709991 9.89570197,10.709991 Z M8.98919546,9.04212824 C9.09790709,9.14792278 9.15884755,9.29158681 9.1585213,9.44110085 C9.15829001,9.59073155 9.09678989,9.73407335 8.98763252,9.83954568 C8.87847514,9.945018 8.73069852,10.0039347 8.57678157,10.0033977 C8.42286747,10.0027392 8.27565088,9.94273467 8.16727355,9.83639845 C8.05900765,9.73006224 7.99873866,9.58628988 7.99963013,9.43664806 C8.00052304,9.28788403 8.0620221,9.14542556 8.17051087,9.04048101 C8.27911107,8.93555591 8.42599335,8.87663641 8.57913312,8.87663641 C8.73291864,8.87665585 8.88047525,8.93622535 8.98919546,9.04212824 Z M7.99965585,17.9999981 C4.91377349,17.9999981 3.29882839,17.7332867 2.51364277,17.4999976 C2.37780966,17.4476975 2.26954376,17.3439641 2.21396931,17.2125528 C2.15838628,17.0811499 2.16006066,16.9334692 2.21876871,16.8033858 C2.6144474,15.5921346 3.14916224,14.4280501 3.81316983,13.3333824 C5.980145,9.82337899 8.22941036,13.8867718 10.0980836,13.8867718 C11.9666996,13.8867718 11.4695868,12.1534924 12.1827971,13.3333824 C12.8511505,14.4269112 13.3916656,15.5896902 13.794259,16.8000524 C13.8533022,16.9322137 13.8537479,17.0822749 13.7952635,17.2147751 C13.7368889,17.3472613 13.6248314,17.4504531 13.4856467,17.5000531 C12.6833967,17.7332867 11.0855382,17.9999981 7.99965585,17.9999981 Z"
+            id="Shape"></path>
+        </g>
+      </g>
+    </svg>
+  );
+});
diff --git a/src/components/Layout/Page.tsx b/src/components/Layout/Page.tsx
index 1040e1aa7b..ec3a6eba0c 100644
--- a/src/components/Layout/Page.tsx
+++ b/src/components/Layout/Page.tsx
@@ -31,7 +31,7 @@ interface PageProps {
   meta: {
     title?: string;
     titleForTitleTag?: string;
-    canary?: boolean;
+    version?: 'experimental' | 'canary';
     description?: string;
   };
   section: 'learn' | 'reference' | 'community' | 'blog' | 'home' | 'unknown';
@@ -53,7 +53,7 @@ export function Page({
     routeTree
   );
   const title = meta.title || route?.title || '';
-  const canary = meta.canary || false;
+  const version = meta.version;
   const description = meta.description || route?.description || '';
   const isHomePage = cleanedPath === '/';
   const isBlogIndex = cleanedPath === '/blog';
@@ -70,7 +70,7 @@ export function Page({
           )}>
           <PageHeading
             title={title}
-            canary={canary}
+            version={version}
             description={description}
             tags={route?.tags}
             breadcrumbs={breadcrumbs}
diff --git a/src/components/Layout/Sidebar/SidebarLink.tsx b/src/components/Layout/Sidebar/SidebarLink.tsx
index 4429989d2f..aadb6cf4de 100644
--- a/src/components/Layout/Sidebar/SidebarLink.tsx
+++ b/src/components/Layout/Sidebar/SidebarLink.tsx
@@ -9,6 +9,7 @@ import * as React from 'react';
 import cn from 'classnames';
 import {IconNavArrow} from 'components/Icon/IconNavArrow';
 import {IconCanary} from 'components/Icon/IconCanary';
+import {IconExperimental} from 'components/Icon/IconExperimental';
 import Link from 'next/link';
 
 interface SidebarLinkProps {
@@ -16,7 +17,7 @@ interface SidebarLinkProps {
   selected?: boolean;
   title: string;
   level: number;
-  version?: 'canary' | 'major';
+  version?: 'canary' | 'major' | 'experimental';
   icon?: React.ReactNode;
   isExpanded?: boolean;
   hideArrow?: boolean;
@@ -84,7 +85,13 @@ export function SidebarLink({
         )}
         {version === 'canary' && (
           <IconCanary
-            title=" - This feature is available in the latest Canary"
+            title=" - This feature is available in the latest Canary version of React"
+            className="ms-1 text-gray-30 dark:text-gray-60 inline-block w-3.5 h-3.5 align-[-3px]"
+          />
+        )}
+        {version === 'experimental' && (
+          <IconExperimental
+            title=" - This feature is available in the latest Experimental version of React"
             className="ms-1 text-gray-30 dark:text-gray-60 inline-block w-3.5 h-3.5 align-[-3px]"
           />
         )}
diff --git a/src/components/MDX/ExpandableCallout.tsx b/src/components/MDX/ExpandableCallout.tsx
index 9d39298591..5317009a12 100644
--- a/src/components/MDX/ExpandableCallout.tsx
+++ b/src/components/MDX/ExpandableCallout.tsx
@@ -16,6 +16,7 @@ type CalloutVariants =
   | 'note'
   | 'wip'
   | 'canary'
+  | 'experimental'
   | 'major'
   | 'rsc';
 
@@ -51,6 +52,15 @@ const variantMap = {
     overlayGradient:
       'linear-gradient(rgba(245, 249, 248, 0), rgba(245, 249, 248, 1)',
   },
+  experimental: {
+    title: 'Experimental Feature',
+    Icon: IconCanary,
+    containerClasses:
+      'bg-green-5 dark:bg-green-60 dark:bg-opacity-20 text-primary dark:text-primary-dark text-lg',
+    textColor: 'text-green-60 dark:text-green-40',
+    overlayGradient:
+      'linear-gradient(rgba(245, 249, 248, 0), rgba(245, 249, 248, 1)',
+  },
   pitfall: {
     title: '陷阱',
     Icon: IconPitfall,
diff --git a/src/components/MDX/MDXComponents.tsx b/src/components/MDX/MDXComponents.tsx
index f4586ad759..24220873dc 100644
--- a/src/components/MDX/MDXComponents.tsx
+++ b/src/components/MDX/MDXComponents.tsx
@@ -98,6 +98,10 @@ const Canary = ({children}: {children: React.ReactNode}) => (
   <ExpandableCallout type="canary">{children}</ExpandableCallout>
 );
 
+const Experimental = ({children}: {children: React.ReactNode}) => (
+  <ExpandableCallout type="experimental">{children}</ExpandableCallout>
+);
+
 const NextMajor = ({children}: {children: React.ReactNode}) => (
   <ExpandableCallout type="major">{children}</ExpandableCallout>
 );
@@ -120,6 +124,20 @@ const CanaryBadge = ({title}: {title: string}) => (
   </span>
 );
 
+const ExperimentalBadge = ({title}: {title: string}) => (
+  <span
+    title={title}
+    className={
+      'text-base font-display px-1 py-0.5 font-bold bg-gray-10 dark:bg-gray-60 text-gray-60 dark:text-gray-10 rounded'
+    }>
+    <IconCanary
+      size="s"
+      className={'inline me-1 mb-0.5 text-sm text-gray-60 dark:text-gray-10'}
+    />
+    Experimental only
+  </span>
+);
+
 const NextMajorBadge = ({title}: {title: string}) => (
   <span
     title={title}
@@ -508,6 +526,8 @@ export const MDXComponents = {
   MathI,
   Note,
   Canary,
+  Experimental,
+  ExperimentalBadge,
   CanaryBadge,
   NextMajor,
   NextMajorBadge,
diff --git a/src/components/PageHeading.tsx b/src/components/PageHeading.tsx
index 6000c8e51d..409bd03b8e 100644
--- a/src/components/PageHeading.tsx
+++ b/src/components/PageHeading.tsx
@@ -8,10 +8,12 @@ import {H1} from './MDX/Heading';
 import type {RouteTag, RouteItem} from './Layout/getRouteMeta';
 import * as React from 'react';
 import {IconCanary} from './Icon/IconCanary';
+import {IconExperimental} from './Icon/IconExperimental';
 
 interface PageHeadingProps {
   title: string;
-  canary?: boolean;
+  version?: 'experimental' | 'canary';
+  experimental?: boolean;
   status?: string;
   description?: string;
   tags?: RouteTag[];
@@ -21,19 +23,26 @@ interface PageHeadingProps {
 function PageHeading({
   title,
   status,
-  canary,
+  version,
   tags = [],
   breadcrumbs,
 }: PageHeadingProps) {
+  console.log('version', version);
   return (
     <div className="px-5 sm:px-12 pt-3.5">
       <div className="max-w-4xl ms-0 2xl:mx-auto">
         {breadcrumbs ? <Breadcrumbs breadcrumbs={breadcrumbs} /> : null}
         <H1 className="mt-0 text-primary dark:text-primary-dark -mx-.5 break-words">
           {title}
-          {canary && (
+          {version === 'canary' && (
             <IconCanary
-              title=" - This feature is available in the latest Canary"
+              title=" - This feature is available in the latest Canary version of React"
+              className="ms-4 mt-1 text-gray-50 dark:text-gray-40 inline-block w-6 h-6 align-[-1px]"
+            />
+          )}
+          {version === 'experimental' && (
+            <IconExperimental
+              title=" - This feature is available in the latest Experimental version of React"
               className="ms-4 mt-1 text-gray-50 dark:text-gray-40 inline-block w-6 h-6 align-[-1px]"
             />
           )}
diff --git a/src/content/blog/2025/04/01/react-labs-what-we-have-been-working-on-april-2025.md b/src/content/blog/2025/04/01/react-labs-what-we-have-been-working-on-april-2025.md
new file mode 100644
index 0000000000..5426f4584e
--- /dev/null
+++ b/src/content/blog/2025/04/01/react-labs-what-we-have-been-working-on-april-2025.md
@@ -0,0 +1,12993 @@
+---
+title: "React Labs: What We've Been Working On – April 2025"
+author: Ricky Hanlon,  Lauren Tan, Mofei Zhang, Jordan Eldredge, Jack Pope, Matt Carroll
+date: 2025/04/01
+description: TODO
+---
+
+April 1, 2025 by [Ricky Hanlon](https://twitter.com/rickhanlonii), and [Matt Carroll](https://twitter.com/mattcarrollcode).
+
+---
+
+<Intro>
+
+In React Labs posts, we write about projects in active research and development. In this post, we're sharing two new experimental features that are ready to try today, and updates on other areas we're working on now.
+
+</Intro>
+
+
+<Note>
+
+React Conf 2025 is scheduled for October 7–8 in Henderson, Nevada! 
+
+We're looking for speakers to help us create talks about the features covered in this post. If you're interested in speaking at ReactConf, [please apply here](https://forms.reform.app/react-conf/call-for-speakers/piaae1?ga4_visitor_id=c3e8f3ce-2004-47a5-b801-f6b308280acd) (no talk proposal required).
+
+For more info on tickets, free streaming, sponsoring, and more, see [the React Conf website](https://conf.react.dev).
+
+</Note>
+
+Today, we're excited to release documentation for two new experimental features that are ready for testing:
+
+- [View Transitions](#view-transitions)
+- [Activity](#activity)
+
+We're also sharing updates on new features currently in development:
+- [React Performance Tracks](#react-performance-tracks)
+- [Compiler IDE Extension](#compiler-ide-extension)
+- [Automatic Effect Dependencies](#automatic-effect-dependencies)
+- [Fragment Refs](#fragment-refs)
+- [Concurrent stores](#concurrent-stores)
+
+---
+
+# New Experimental Features {/*new-experimental-features*/}
+
+View Transitions and Activity are now ready for testing in `react@experimental`.These features have been tested in production and are stable, but the final API may still change as we incorporate feedback.
+
+
+
+You can try them by upgrading React packages to the most recent experimental version:
+
+- `react@experimental`
+- `react-dom@experimental`
+
+Read on to learn how to use these features in your app, or check out the newly published docs:
+
+- [`<ViewTransition>`](/reference/react/ViewTransition): A component lets you activate an animation for a Transition.
+- [`addTransitionType`](/reference/react/addTransitionType): A function that allows you to specify the cause of a Transition.
+- [`<Activity>`](/reference/react/Activity): A component that lets you hide and show part of the UI.
+
+## View Transitions {/*view-transitions*/}
+
+React View Transitions are a new experimental feature that makes it easier to add animations to UI transitions in your app. Under-the-hood, these animations APIs use the new [`startViewTransition`](https://developer.mozilla.org/en-US/docs/Web/API/Document/startViewTransition) API available in most modern browsers.
+
+To opt-in to animating an element, wrap it in the new `<ViewTransition>` component:
+
+
+```js
+// "what" to animate.
+<ViewTransition>
+  <div>animate me</div>
+</ViewTransition>
+```
+
+This new component lets you declaratively define "what" to animate when an animation is activated. 
+
+You can define "when" to animate by using one of these three triggers for a View Transition:
+
+```js
+// "when" to animate.
+
+// Transitions
+startTransition(() => setState(...));
+
+// Deferred Values
+const deferred = useDeferredValue(value);
+
+// Suspense
+<Suspense fallback={<Fallback />}>
+  <div>Loading...</div>
+</Suspense>
+```
+
+By default, these animations use the [default CSS animations for View Transitions](https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API/Using#customizing_your_animations) applied (typically a smooth cross-fade). You can use [view transition pseudo-selectors](https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API/Using#the_view_transition_pseudo-element_tree) to define "how" the animation runs. For example, you can use `*` to change the default animation for all transitions:
+
+```
+// "how" to animate.
+::view-transition-old(*) {
+  animation: 300ms ease-out fade-out;
+}
+::view-transition-new(*) {
+  animation: 300ms ease-in fade-in;
+}
+```
+
+When the DOM updates due to an animation trigger&mdash;like `startTransition`, `useDeferredValue`, or a `Suspense` fallback switching to content&mdash;React will use [declarative heuristics](/reference/react/ViewTransition#viewtransition) to automatically determine which `<ViewTransition>` components to activate for the animation. The browser will then run the animation that's defined in CSS.
+
+If you're familiar with the browser's View Transition API and want to know how React supports it, check out [How does `<ViewTransition>` Work](/reference/react/ViewTransition#how-does-viewtransition-work) in the docs. 
+
+In this post, let's take a look at a few examples of how to use View Transitions. 
+
+We'll start with this app, which doesn't animate any of the following interactions:
+- Click a video to view the details.
+- Click "back" to go back to the feed.
+- Type in the list to filter the videos.
+
+<Sandpack>
+
+```js src/App.js active
+import TalkDetails from './Details'; import Home from './Home'; import {useRouter} from './router';
+
+export default function App() {
+  const {url} = useRouter();
+
+  // 🚩This version doesn't include any animations yet
+  return url === '/' ? <Home /> : <TalkDetails />;
+}
+```
+
+```js src/Details.js
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js
+import { useState } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    >
+      {children}
+    </div>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {
+  useState,
+  createContext,
+  use,
+  useTransition,
+  useLayoutEffect,
+  useEffect,
+} from "react";
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+export function Router({ children }) {
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  const [isPending, startTransition] = useTransition();
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  function navigateBack(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+```
+
+```css src/styles.css
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+<Note>
+
+#### View Transitions do not replace CSS and JS driven animations {/*view-transitions-do-not-replace-css-and-js-driven-animations*/}
+
+View Transitions are meant to be used for UI transitions such as navigation, expanding, opening, or re-ordering. They are not meant to replace all the animations in your app.
+
+In our example app above, notice that there are already animations when you click the "like" button and the Suspense fallback glimmer. These are good use cases for CSS animations because they are animating a specific element.
+
+</Note>
+
+### Animating navigations {/*animating-navigations*/}
+
+Our app includes a Suspense-enabled router, with [page transitions already marked as Transitions](/reference/react/useTransition#building-a-suspense-enabled-router), which means navigations are performed with `startTransition`:
+
+```js
+function navigate(url) {
+  startTransition(() => {
+    go(url);
+  });
+}
+```
+
+`startTransition` is a View Transition trigger, so we can add `<ViewTransition>` to animate between pages:
+
+```js
+// "what" to animate
+<ViewTransition key={url}>
+  {url === '/' ? <Home /> : <TalkDetails />}
+</ViewTransition>
+```
+
+When the `url` changes, the `<ViewTransition>` and new route are rendered. Since the `<ViewTransition>` was updated inside of `startTransition`, the `<ViewTransition>` is activated for an animation.
+
+
+By default, View Transitions include the browser default cross-fade animation. Adding this to our example, we now have a cross-fade whenever we navigate between pages: 
+
+<Sandpack>
+
+```js src/App.js active
+import {unstable_ViewTransition as ViewTransition} from 'react'; import Details from './Details'; import Home from './Home'; import {useRouter} from './router';
+
+export default function App() {
+  const {url} = useRouter();
+  
+  // Use ViewTransition to animate between pages.
+  // No additional CSS needed by default.
+  return (
+    <ViewTransition>
+      {url === '/' ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    >
+      {children}
+    </div>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {useState, createContext,use,useTransition,useLayoutEffect,useEffect} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+  
+  
+  
+  
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+
+  function navigateBack(url) {
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+Since our router already updates the route using `startTransition`, this one line change to add `<ViewTransition>` activates with the default cross-fade animation. 
+
+If you're curious how this works, see the docs for [How does `<ViewTransition>` work?](/reference/react/ViewTransition#how-does-viewtransition-work)
+
+### Customizing animations {/*customizing-animations*/}
+
+By default, `<ViewTransition>` includes the default cross-fade from the browser.
+
+To customize animations, you can provide props to the `<ViewTransition>` component to specify which animations to use, based on [how the `<ViewTransition>` activates](/reference/react/ViewTransition#props).
+
+For example, we can slow down the `default` cross fade animation:
+
+```js
+<ViewTransition default="slow-fade">
+  <Home />
+</ViewTransition>
+```
+
+And define `slow-fade` in CSS using [view transition classes](/reference/react/ViewTransition#view-transition-classes):
+
+```css
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+Now, the cross fade is slower:
+
+<Sandpack>
+
+```js src/App.js active
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Define a default animation of .slow-fade.
+  // See animations.css for the animation definiton.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === '/' ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    >
+      {children}
+    </div>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {
+  useState,
+  createContext,
+  use,
+  useTransition,
+  useLayoutEffect,
+  useEffect,
+} from "react";
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+export function Router({ children }) {
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  const [isPending, startTransition] = useTransition();
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  function navigateBack(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Define .slow-fade using view transition classes */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+See [Styling View Transitions](/reference/react/ViewTransition#styling-view-transitions) for a full guide on styling `<ViewTransition>`.
+
+### Shared Element Transitions {/*shared-element-transitions*/}
+
+When two pages include the same element, often you want to animate it from one page to the next.
+
+To do this you can add a unique `name` to the `<ViewTransition>`:
+
+```js
+<ViewTransition name={`video-${video.id}`}>
+  <Thumbnail video={video} />
+</ViewTransition>
+```
+
+Now the video thumbnail animates between the two pages:
+
+<Sandpack>
+
+```js src/App.js
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Keeping our default slow-fade.
+  // This allows the content not in the shared
+  // element transition to cross-fade.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js active
+import { useState, unstable_ViewTransition as ViewTransition } from "react"; import LikeButton from "./LikeButton"; import { useRouter } from "./router"; import { PauseIcon, PlayIcon } from "./Icons"; import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {
+  useState,
+  createContext,
+  use,
+  useTransition,
+  useLayoutEffect,
+  useEffect,
+} from "react";
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+export function Router({ children }) {
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  const [isPending, startTransition] = useTransition();
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  function navigateBack(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+By default, React automatically generates a unique `name` for each element activated for a transition (see [How does `<ViewTransition>` work](/reference/react/ViewTransition#how-does-viewtransition-work)). When React sees a transition where a `<ViewTransition>` with a `name` is removed and a new `<ViewTransition>` with the same `name` is added, it will activate a shared element transition.
+
+For more info, see the docs for [Animating a Shared Element](/reference/react/ViewTransition#animating-a-shared-element).
+
+### Animating based on cause {/*animating-based-on-cause*/}
+
+Sometimes, you may want elements to animate differently based on how it was triggered. For this use case, we've added a new API called `addTransitionType` to specify the cause of a transition:
+
+```js {4,11}
+function navigate(url) {
+  startTransition(() => {
+    // Transition type for the cause "nav forward"
+    addTransitionType('nav-forward');
+    go(url);
+  });
+}
+function navigateBack(url) {
+  startTransition(() => {
+    // Transition type for the cause "nav backward"
+    addTransitionType('nav-back');
+    go(url);
+  });
+}
+```
+
+With transition types, you can provide custom animations via props to `<ViewTransition>`. Let's add a shared element transition to the header for "6 Videos" and "Back":
+
+```js {4,5}
+<ViewTransition
+  name="nav"
+  share={{
+    'nav-forward': 'slide-forward',
+    'nav-back': 'slide-back',
+  }}>
+  {heading}
+</ViewTransition>
+```
+
+Here we pass a `share` prop to define how to animate based on the transiton type. When the share transition activates from `nav-forward`, the view transition class `slide-forward` is applied. When it's from `nav-back`, the `slide-back` animation is activated. Let's define these animations in CSS:
+
+```css
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: ...
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: ...
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: ...
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: ...
+}
+```
+
+Now we can animate the header along with thumbnail based on navigation type:
+
+<Sandpack>
+
+```js src/App.js hidden
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Keeping our default slow-fade.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js active
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* New keyframes to support our animations above. */
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Previously defined animations. */
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+### Animating Suspense Boundaries {/*animating-suspense-boundaries*/}
+
+Suspense will also activate `<ViewTransition>` when the fallback is replaced by content. This is why the video description currently fades in with our `slow-fade` animation after the Suspense fallback.
+
+We can customize the Suspense animation using an `exit` on the fallback, and `enter` on the content:
+
+```js {3,8}
+<Suspense
+  fallback={
+    <ViewTransition exit="slide-down">
+      <VideoInfoFallback />
+    </ViewTransition>
+  }
+>
+  <ViewTransition enter="slide-up">
+    <VideoInfo id={id} />
+  </ViewTransition>
+</Suspense>
+```
+
+Here's how we'll define `slide-down` and `slide-up` with CSS:
+
+```css {1, 6}
+::view-transition-old(.slide-down) { 
+  /* Slide the fallback down */
+  animation: ...;
+}
+
+::view-transition-new(.slide-up) {
+  /* Slide the content up */
+  animation: ...;
+}
+```
+
+Now, the Suspense content replaces the fallback with a sliding animation:
+
+<Sandpack>
+
+```js src/App.js hidden
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Default slow-fade animation.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js active
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react"; import { fetchVideo, fetchVideoDetails } from "./data"; import { Thumbnail, VideoControls } from "./Videos"; import { useRouter } from "./router"; import Layout from "./Layout"; import { ChevronLeft } from "./Icons";
+
+function VideoDetails({ id }) {
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Slide the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+/* Slide the content up */
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Define the new keyframes */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+/* Previously defined animations below */
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+
+### Animating Lists {/*animating-lists*/}
+
+You can also use `<ViewTransition>` to animate lists of items as they re-order, like in a searchable list of items:
+
+```js {3,5}
+<div className="videos">
+  {filteredVideos.map((video) => (
+    <ViewTransition key={video.id}>
+      <Video video={video} />
+    </ViewTransition>
+  ))}
+</div>
+```
+
+To activate the ViewTransition, we can use `useDeferredValue`:
+
+```js {2}
+const [searchText, setSearchText] = useState('');
+const deferredSearchText = useDeferredValue(searchText);
+const filteredVideos = filterVideos(videos, deferredSearchText);
+```
+
+Now the items animate as you type in the search bar:
+
+<Sandpack>
+
+```js src/App.js hidden
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Default slow-fade animation.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react";
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+
+/* Slide animation for Suspense */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+### Final result {/*final-result*/}
+
+By adding a few `<ViewTransition>` components and a few lines of CSS, we were able to add all the animations above into the final result.
+
+We're excited about View Transitions and think they will level up the apps you're able to build. They're ready to start trying today in the experimental channel of React releases.
+
+Let's remove the slow fade, and take a look at the final result:
+
+<Sandpack>
+
+```js src/App.js
+import {unstable_ViewTransition as ViewTransition} from 'react'; import Details from './Details'; import Home from './Home'; import {useRouter} from './router';
+
+export default function App() {
+  const {url} = useRouter();
+
+  // Animate with a cross fade between pages.
+  return (
+    <ViewTransition key={url}>
+      {url === '/' ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react"; import { fetchVideo, fetchVideoDetails } from "./data"; import { Thumbnail, VideoControls } from "./Videos"; import { useRouter } from "./router"; import Layout from "./Layout"; import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js
+import { useState, unstable_ViewTransition as ViewTransition } from "react"; import LikeButton from "./LikeButton"; import { useRouter } from "./router"; import { PauseIcon, PlayIcon } from "./Icons"; import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Slide animations for Suspense the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+If you're curious to know more about how they work, check out [How Does `<ViewTransition>` Work](/reference/react/ViewTransition#how-does-viewtransition-work) in the docs.
+
+_For more background on how we built View Transitions, see: [#31975](https://github.com/facebook/react/pull/31975), [#32105](https://github.com/facebook/react/pull/32105), [#32041](https://github.com/facebook/react/pull/32041), [#32734](https://github.com/facebook/react/pull/32734), [#32797](https://github.com/facebook/react/pull/32797) [#31999](https://github.com/facebook/react/pull/31999), [#32031](https://github.com/facebook/react/pull/32031), [#32050](https://github.com/facebook/react/pull/32050), [#32820](https://github.com/facebook/react/pull/32820), [#32029](https://github.com/facebook/react/pull/32029), [#32028](https://github.com/facebook/react/pull/32028), and [#32038](https://github.com/facebook/react/pull/32038) by [@sebmarkbage](https://twitter.com/sebmarkbage) (thanks Seb!)._
+
+---
+
+## Activity {/*activity*/}
+
+In [past](/blog/2022/06/15/react-labs-what-we-have-been-working-on-june-2022#offscreen) [updates](/blog/2024/02/15/react-labs-what-we-have-been-working-on-february-2024#offscreen-renamed-to-activity), we shared that we were researching an API to allow components to be visually hidden and deprioritized, preserving UI state with reduced performance costs relative to unmounting or hiding with CSS.
+
+We're now ready to share the API and how it works, so you can start testing it in experimental React versions.
+
+`<Activity>` is a new component to hide and show parts of the UI:
+
+```js [[1, 1, "'visible'"], [2, 1, "'hidden'"]]
+<Activity mode={isVisible ? 'visible' : 'hidden'}>
+  <Page />
+</Activity>
+```
+
+When an Activity is <CodeStep step={1}>visible</CodeStep> it's rendered as normal. When an Activity is <CodeStep step={2}>hidden</CodeStep> it is unmounted, but will save it's state and continue to render at a lower priority than anything visible on screen.
+
+You can use `Activity` save state for parts of the UI the user isn't using, or pre-render parts that a user is likely to use next.
+
+Let's look at some examples improving the View Transition examples above.
+
+<Note>
+
+**Effects don’t mount when an Activity is hidden.**
+
+When an `<Activity>` is `hidden`, Effects are unmounted. Conceptually, the component is unmounted, but React saves the state for later.
+
+In practice, this works as expected if you have followed the [You Might Not Need an Effect](/learn/you-might-not-need-an-effect) guide. To eagerly find problematic Effects, we recommend adding [`<StrictMode>`](/reference/react/StrictMode) which will eagerly perform Activity unmounts and mounts to catch any unexpected side effects.
+
+</Note>
+
+### Restoring state with Activity {/*restoring-state-with-activity*/}
+
+When a user navigates away from a page, it's common to stop rendering the old page:
+
+```js {6,7}
+function App() {
+  const { url } = useRouter();
+  
+  return (
+    <>
+      {url === '/' && <Home />}
+      {url !== '/' && <Details />}
+    </>
+  );
+}
+```
+
+However, this means if the user goes back to the old page, all of the previous state is lost. For example, if the `<Home />` page has an `<input>` field, when the user leaves the page the `<input`> is unmouted, and all of the text they had typed is lost.
+
+Activity allows you to keep the state around as the user changes pages, so when they come back they can resume where they left off. This is done by wrapping part of the tree in `<Activity>` and toggling the `mode`:
+
+```js {6-8}
+function App() {
+  const { url } = useRouter();
+  
+  return (
+    <>
+      <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+        <Home />
+      </Activity>
+      {url !== '/' && <Details />}
+    </>
+  );
+}
+```
+
+With this change, we can improve on our View Transitons example above. Before, when you searched for a video, selected one, and returned, your search filter was lost. With Activity, your search filter is restored and you can pick up where you left off.
+
+Try searching for a video, selecting it, and clicking "back":
+
+<Sandpack>
+
+```js src/App.js
+import { unstable_ViewTransition as ViewTransition, unstable_Activity as Activity } from "react"; import Details from "./Details"; import Home from "./Home"; import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+  
+  return (
+    // View Transitions know about Activity
+    <ViewTransition>
+      {/* Render Home in Activity so we don't lose state */}
+      <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+        <Home />
+      </Activity>
+      {url !== '/' && <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react";
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js hidden
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+
+/* Slide animations for Suspense the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+### Pre-rendering with Activity {/*prerender-with-activity*/}
+
+Sometimes, you may want to prepare the next part of the UI a user is likely to use ahead of time, so it's ready by the time they are ready to use it. This is especially useful if the next route needs to suspend on data it needs to render, because you can help ensure the data is already fetched before the user navigates.
+
+For example, our app currently needs to suspend to load the data for each video when you select one. We can improve this by rendering all of the pages is a hidden `<Activity>` until the user navigates:
+
+```js {2,5,8}
+<ViewTransition>
+  <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+    <Home />
+  </Activity>
+  <Activity mode={url === '/details/1' ? 'visible' : 'hidden'}>
+    <Details id={id} />
+  </Activity>
+  <Activity mode={url === '/details/1' ? 'visible' : 'hidden'}>
+    <Details id={id} />
+  </Activity>
+<ViewTransition>
+```
+
+With this update, if you select a video after 1 second, the content has time to pre-render and animates without the Suspense fallback:
+
+<Sandpack>
+
+```js src/App.js
+import { unstable_ViewTransition as ViewTransition, unstable_Activity as Activity, use } from "react"; import Details from "./Details"; import Home from "./Home"; import { useRouter } from "./router"; import {fetchVideos} from './data'
+
+export default function App() {
+  const { url } = useRouter();
+  const videoId = url.split("/").pop();
+  const videos = use(fetchVideos());
+  
+  return (
+    <ViewTransition>
+      {/* Render videos in Activity to pre-render them */}
+      {videos.map(({id}) => (
+        <Activity key={id} mode={videoId === id ? 'visible' : 'hidden'}>
+          <Details id={id}/>
+        </Activity>
+      ))}
+      <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+        <Home />
+      </Activity>
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react";
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details({id}) {
+  const { url, navigateBack } = useRouter();
+  const video = use(fetchVideo(id));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js hidden
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+
+/* Slide animations for Suspense the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+---
+
+# Features in development {/*features-in-development*/}
+
+## React Performance Tracks {/*react-performance-tracks*/}
+
+We're working on a new set of custom tracks to performance profilers using browser APIs that [allow adding custom tracks](https://developer.chrome.com/docs/devtools/performance/extension) to provide more information about the performance of your React app.
+
+This feature is still in progress, so we're not ready to publish docs to fully release it as an experimental feature yet. You can get a sneak preview when using an experimental version of React, which will automatically see the performance tracks added to profiles:
+
+<div style={{display: 'flex', justifyContent: 'center', marginBottom: '1rem'}}>
+  <picture >
+      <source srcset="/images/blog/react-labs-april-2025/perf_tracks.png" />
+      <img className="w-full light-image" src="/images/blog/react-labs-april-2025/perf_tracks.webp" />
+  </picture>
+  <picture >
+      <source srcset="/images/blog/react-labs-april-2025/perf_tracks_dark.png" />
+      <img className="w-full dark-image" src="/images/blog/react-labs-april-2025/perf_tracks_dark.webp" />
+  </picture>
+</div>
+
+There are a few known issues we plan to address such as performance, and the scheduler track not always "connecting" work across Suspended trees, so it's not quite ready to try. We're also still collecting feedback from early adopters to improve the design and usability of the tracks.
+
+Once we solve those issues, we'll publish experimental docs and share that it's ready to try.
+
+---
+
+## Compiler IDE Extension {/*compiler-ide-extension*/}
+
+Earlier this week [we shared](/blog/2025/04/21/react-compiler-rc) the React Compiler release candidate, and we're working towards shipping the first SemVer stable version of the compiler in the coming months.
+
+We've also begun exploring ways to use the React Compiler to provide information that can improve understanding and debugging your code. One idea we've started exploring is a new experimental LSP-based React IDE extension powered by React Compiler, similar to the extension used in [Lauren Tan's React Conf talk](https://conf2024.react.dev/talks/5).
+
+Our idea is that we can use the compiler's static analysis to provide more information, suggestions, and optimization opportunities directly in your IDE. For example, we can provide diagnostics for code breaking the Rules of React, hovers to show if components and hooks were optimized by the compiler, or a CodeLens to see [automatically inserted Effect dependencies](/#automatic-effect-dependencies).
+
+The IDE extension is still an early exploration, but we'll share our progress in future updates.
+
+---
+
+## Automatic Effect Dependencies {/*automatic-effect-dependencies*/}
+
+When we released hooks, we had three motivations:
+
+- **Sharing code between components**: hooks replaced patterns like render props and higher-order components to allow you to reuse stateful logic without changing your component hierarchy.
+- **Think in terms of function, not lifecycles**: hooks let you split one component into smaller functions based on what pieces are related (such as setting up a subscription or fetching data), rather than forcing a split based on lifecycle methods.
+- **Support ahead-of-time compilation**: hooks were designed to support ahead-of-time compilation with less pitfalls causing unintention de-optimizations caused by lifecycle methods, and limitation of classes.
+
+Since their release, hooks have been successful at *sharing code between components*. Hooks are now the favored way to share logic between components, and there are less use cases for render props and higher order components. Hooks have also been successful at supporting features like Fast Refresh that were not possible with class components. 
+
+### Effects can be hard {/*effects-can-be-hard*/}
+
+Unfortunately, some hooks are still hard to think in terms of function instead of lifecycles. Effects specifically are still hard to understand and is the most common pain point we hear from developers. Last year, we spent a significant amount of time researching how effects were used, and how those use cases could be simplified and easier to understand.
+
+We found that often, the confusion is from using an Effect when you don't need to. The [You Probably Don't Need an Effect guide](/TODO), covers many cases for when Effects are not the right solution. However, even when an Effect is the right fit for a problem, Effects can still be harder to understand than class component lifecyles.
+
+We believe one of the reasons for confusion is the dependency array, which allows developers to think of effects from the _components_ perspective (like a lifecycle), instead of the _effects_ point of view (what the effect does).
+
+Let's look at an example [from the docs](/learn/lifecycle-of-reactive-effects#thinking-from-the-effects-perspective):
+
+```js
+useEffect(() => {
+  // Your Effect connected to the room specified with roomId...
+  const connection = createConnection(serverUrl, roomId);
+  connection.connect();
+  return () => {
+    // ...until it disconnected
+    connection.disconnect();
+  };
+}, [roomId]);
+```
+
+Many users would read this code as "on mount, connect to the roomId. whenever `roomId` changes, disconnect to the old room and re-create the connection". However, this is thinking from the component's lifecycle perspective, which means you will need to think of every component lifecycle state to write the effect correctly. This can be difficult, so it's understandble that Effects seem harder than class lifecycles when using component perspective.
+
+### Effects without dependencies {/*effects-without-dependencies*/}
+
+Instaed, it's better to think from the Effect's perspective. The effect doesn't know about about the component lifecycles. It only describes how to start synchronization and how to stop it. When users think of Effects in this way, their Effects tend to be easier to write, and more resilient to being started and stopped as many times as it’s needed.
+
+We spent some time researching why Effects are thought of from the component perspective, and we think one of the resons is the dependency array. Since you have to write it, it's right there and in your face reminding you of what you're "reacting" to and baiting you into the mental model of 'do this when these values change'.
+
+When we released hooks, we knew we could make them easier to use with ahead-of-time compilation. With the React Compiler, you're now able to avoid writing `useCallback` and `useMemo` yourself in most cases. For Effects, the compiler can insert the dependencies for you:
+
+```js
+useEffect(() => {
+  const connection = createConnection(serverUrl, roomId);
+  connection.connect();
+  return () => {
+    connection.disconnect();
+  };
+}); // compiler inserted dependencies. 
+```
+
+With this code, the React Compiler can infer the dependencies for you and insert them automatically so you don't need to see or write them. With features like the IDE exension and `useEffectEvent`, we can provide a CodeLens to show you what the Compiler inserted for times you need to debug, or to optimize by removing a dependency. This helps reinforce the correct mental model for writing Effects, which can run at any time to synchronize your component or hook's state with something else
+
+Our hope is that automatically inserting dependencies is not only easier to write, but that it also makes them easier to understand by forcing you to think in terms of what the effect does, and not in component lifecycles. 
+
+---
+
+## Fragment Refs {/*fragment-refs*/}
+
+Many DOM APIs like those for event management, positioning, and focus are difficult to compose when writing with React. This often leads developers to reach for Effects, managing multiple Refs, or APIs like `findDOMNode` (removed in React 19).
+
+We are exploring adding refs to Fragments that would point to a group of DOM elements, rather than just a single element. Our hope is that this will simplify managing multiple children and make it easier to write composable React code when calling DOM APIs.
+
+Fragment refs are still being researched. We'll share more when we're closer to having the final API finished.
+
+---
+
+## Gesture Animations {/*gesture-animations*/}
+
+We're also researching ways to enhance View Transitions to support gesture animations such as swiping to open a menu, or scroll through a photo carousel. 
+
+Gestures present new challenges for a few reasons:
+
+- **Gestures are continuous**: as you swipe the animation is tied to your finger placement time, rather than triggering and running to completion.
+- **Gestures don't complete**: when you release your finger gesture animations can run to completion, or revert to their original state (like when you only partially open a menu) depending on how far you go.
+- **Gestures invert old and new**: while you're animating, you want the page you are animating from to stay "alive" and interactive. This inverts the browser View Transition model where the "old" state is a snapshot and the "new" state is the live DOM.
+
+We believe we’ve found an approach that works well and may introduce a new API for triggering gesture transitions. For now, we're focused on shipping `<ViewTransition>`, and will revisit gestures afterward.
+
+---
+
+## Concurrent stores {/*concurrent-stores*/}
+
+When we released React 18 with concurrent rendering, we also released `useSyncExternalStore` so external store libraries that did not use React state or context could [support concurrent rendering](https://github.com/reactwg/react-18/discussions/70) by forcing a sync render when the store is updated.
+
+Using `useSyncExternalStore` comes at a cost though, since it forces bail out from concurrent features like transitions, and forces existing content to show Suspense fallbacks.
+
+Now that React 19 has shipped, we're re-visiting this problem space to create a primitive to fully support concurrent external stores with the `use` API:
+
+```js
+const value = use(store);
+```
+
+Our goal is to allow external state to be read during render without tearing, and to work seamlessly with all of the concurrent features React offers. 
+
+This research is still early. We'll share more, and what the new APIs will look like, when we're further along. 
+
+---
+
+_TODO: Thanks to [Dan Abramov](https://bsky.app/profile/danabra.mov), [Lauren Tan](https://bsky.app/profile/no.lol), [Jack Pope](https://jackpope.me), [Jason Bonta](https://threads.net/someextent), [Jordan Brown](https://github.com/jbrown215), [Jordan Eldredge](https://bsky.app/profile/capt.dev), and [Mofei Zhang](https://threads.net/z_mofei) for reviewing this post.
diff --git a/src/content/blog/2025/04/21/react-compiler-rc.md b/src/content/blog/2025/04/21/react-compiler-rc.md
index 55c238a93c..9548e57e79 100644
--- a/src/content/blog/2025/04/21/react-compiler-rc.md
+++ b/src/content/blog/2025/04/21/react-compiler-rc.md
@@ -57,23 +57,23 @@ During the RC period, we encourage all React users to try the compiler and provi
 As noted in the Beta announcement, React Compiler is compatible with React 17 and up. If you are not yet on React 19, you can use React Compiler by specifying a minimum target in your compiler config, and adding `react-compiler-runtime` as a dependency. You can find docs on this [here](https://react.dev/learn/react-compiler#using-react-compiler-with-react-17-or-18).
 
 ## Migrating from eslint-plugin-react-compiler to eslint-plugin-react-hooks {/*migrating-from-eslint-plugin-react-compiler-to-eslint-plugin-react-hooks*/}
-If you have already installed eslint-plugin-react-compiler, you can now remove it and use `eslint-plugin-react-hooks@^6.0.0-rc.1`. Many thanks to [@michaelfaith](https://bsky.app/profile/michael.faith) for contributing to this improvement!
+If you have already installed eslint-plugin-react-compiler, you can now remove it and use `eslint-plugin-react-hooks@6.0.0-rc.1`. Many thanks to [@michaelfaith](https://bsky.app/profile/michael.faith) for contributing to this improvement!
 
 To install:
 
 npm
 <TerminalBlock>
-{`npm install --save-dev eslint-plugin-react-hooks@^6.0.0-rc.1`}
+{`npm install --save-dev eslint-plugin-react-hooks@6.0.0-rc.1`}
 </TerminalBlock>
 
 pnpm
 <TerminalBlock>
-{`pnpm add --save-dev eslint-plugin-react-hooks@^6.0.0-rc.1`}
+{`pnpm add --save-dev eslint-plugin-react-hooks@6.0.0-rc.1`}
 </TerminalBlock>
 
 yarn
 <TerminalBlock>
-{`yarn add --dev eslint-plugin-react-hooks@^6.0.0-rc.1`}
+{`yarn add --dev eslint-plugin-react-hooks@6.0.0-rc.1`}
 </TerminalBlock>
 
 ```js
@@ -89,12 +89,14 @@ export default [
 ];
 ```
 
+To enable the React Compiler rule, add `'react-hooks/react-compiler': 'error'` to your ESLint configuration.
+
 The linter does not require the compiler to be installed, so there's no risk in upgrading eslint-plugin-react-hooks. We recommend everyone upgrade today.
 
 ## swc support (experimental) {/*swc-support-experimental*/}
 React Compiler can be installed across [several build tools](/learn/react-compiler#installation) such as Babel, Vite, and Rsbuild.
 
-In addition to those tools, we have been collaborating with Kang Dongyoong ([@kdy1dev](https://x.com/kdy1dev)) from the [swc](https://swc.rs/) team on adding additional support for React Compiler as an swc plugin. As part of the RC release, you can now integrate the compiler into your [Next.js app with swc](https://nextjs.org/docs/app/api-reference/config/next-config-js/reactCompiler) instead of Babel.
+In addition to those tools, we have been collaborating with Kang Dongyoon ([@kdy1dev](https://x.com/kdy1dev)) from the [swc](https://swc.rs/) team on adding additional support for React Compiler as an swc plugin. As part of the RC release, you can now integrate the compiler into your [Next.js app with swc](https://nextjs.org/docs/app/api-reference/config/next-config-js/reactCompiler) instead of Babel.
 
 Next.js users can upgrade to [15.3.1](https://github.com/vercel/next.js/releases/tag/v15.3.1) or greater to try this out. If you have already enabled the compiler in your Next.js's config, swc support will be enabled automatically.
 
diff --git a/src/content/blog/2025/04/23/react-labs-view-transitions-activity-and-more.md b/src/content/blog/2025/04/23/react-labs-view-transitions-activity-and-more.md
new file mode 100644
index 0000000000..7c3ffd7a28
--- /dev/null
+++ b/src/content/blog/2025/04/23/react-labs-view-transitions-activity-and-more.md
@@ -0,0 +1,14358 @@
+---
+title: "React Labs: View Transitions, Activity, and more"
+author: Ricky Hanlon
+date: 2025/04/23
+description: In React Labs posts, we write about projects in active research and development. In this post, we're sharing two new experimental features that are ready to try today, and updates on other areas we're working on now.
+---
+
+April 23, 2025 by [Ricky Hanlon](https://twitter.com/rickhanlonii)
+
+---
+
+<Intro>
+
+In React Labs posts, we write about projects in active research and development. In this post, we're sharing two new experimental features that are ready to try today, and updates on other areas we're working on now.
+
+</Intro>
+
+
+<Note>
+
+React Conf 2025 is scheduled for October 7–8 in Henderson, Nevada! 
+
+We're looking for speakers to help us create talks about the features covered in this post. If you're interested in speaking at ReactConf, [please apply here](https://forms.reform.app/react-conf/call-for-speakers/) (no talk proposal required).
+
+For more info on tickets, free streaming, sponsoring, and more, see [the React Conf website](https://conf.react.dev).
+
+</Note>
+
+Today, we're excited to release documentation for two new experimental features that are ready for testing:
+
+- [View Transitions](#view-transitions)
+- [Activity](#activity)
+
+We're also sharing updates on new features currently in development:
+- [React Performance Tracks](#react-performance-tracks)
+- [Compiler IDE Extension](#compiler-ide-extension)
+- [Automatic Effect Dependencies](#automatic-effect-dependencies)
+- [Fragment Refs](#fragment-refs)
+- [Concurrent Stores](#concurrent-stores)
+
+---
+
+# New Experimental Features {/*new-experimental-features*/}
+
+View Transitions and Activity are now ready for testing in `react@experimental`. These features have been tested in production and are stable, but the final API may still change as we incorporate feedback.
+
+You can try them by upgrading React packages to the most recent experimental version:
+
+- `react@experimental`
+- `react-dom@experimental`
+
+Read on to learn how to use these features in your app, or check out the newly published docs:
+
+- [`<ViewTransition>`](/reference/react/ViewTransition): A component lets you activate an animation for a Transition.
+- [`addTransitionType`](/reference/react/addTransitionType): A function that allows you to specify the cause of a Transition.
+- [`<Activity>`](/reference/react/Activity): A component that lets you hide and show part of the UI.
+
+## View Transitions {/*view-transitions*/}
+
+React View Transitions are a new experimental feature that makes it easier to add animations to UI transitions in your app. Under-the-hood, these animations use the new [`startViewTransition`](https://developer.mozilla.org/en-US/docs/Web/API/Document/startViewTransition) API available in most modern browsers.
+
+To opt-in to animating an element, wrap it in the new `<ViewTransition>` component:
+
+```js
+// "what" to animate.
+<ViewTransition>
+  <div>animate me</div>
+</ViewTransition>
+```
+
+This new component lets you declaratively define "what" to animate when an animation is activated. 
+
+You can define "when" to animate by using one of these three triggers for a View Transition:
+
+```js
+// "when" to animate.
+
+// Transitions
+startTransition(() => setState(...));
+
+// Deferred Values
+const deferred = useDeferredValue(value);
+
+// Suspense
+<Suspense fallback={<Fallback />}>
+  <div>Loading...</div>
+</Suspense>
+```
+
+By default, these animations use the [default CSS animations for View Transitions](https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API/Using#customizing_your_animations) applied (typically a smooth cross-fade). You can use [view transition pseudo-selectors](https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API/Using#the_view_transition_pseudo-element_tree) to define "how" the animation runs. For example, you can use `*` to change the default animation for all transitions:
+
+```
+// "how" to animate.
+::view-transition-old(*) {
+  animation: 300ms ease-out fade-out;
+}
+::view-transition-new(*) {
+  animation: 300ms ease-in fade-in;
+}
+```
+
+When the DOM updates due to an animation trigger&mdash;like `startTransition`, `useDeferredValue`, or a `Suspense` fallback switching to content&mdash;React will use [declarative heuristics](/reference/react/ViewTransition#viewtransition) to automatically determine which `<ViewTransition>` components to activate for the animation. The browser will then run the animation that's defined in CSS.
+
+If you're familiar with the browser's View Transition API and want to know how React supports it, check out [How does `<ViewTransition>` Work](/reference/react/ViewTransition#how-does-viewtransition-work) in the docs. 
+
+In this post, let's take a look at a few examples of how to use View Transitions. 
+
+We'll start with this app, which doesn't animate any of the following interactions:
+- Click a video to view the details.
+- Click "back" to go back to the feed.
+- Type in the list to filter the videos.
+
+<Sandpack>
+
+```js src/App.js active
+import TalkDetails from './Details'; import Home from './Home'; import {useRouter} from './router';
+
+export default function App() {
+  const {url} = useRouter();
+
+  // 🚩This version doesn't include any animations yet
+  return url === '/' ? <Home /> : <TalkDetails />;
+}
+```
+
+```js src/Details.js
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+
+      <div className="bottom">
+        <div className="content">{children}</div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js
+import { useState } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    >
+      {children}
+    </div>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {
+  useState,
+  createContext,
+  use,
+  useTransition,
+  useLayoutEffect,
+  useEffect,
+} from "react";
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+export function Router({ children }) {
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  const [isPending, startTransition] = useTransition();
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  function navigateBack(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+```
+
+```css src/styles.css
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+<Note>
+
+#### View Transitions do not replace CSS and JS driven animations {/*view-transitions-do-not-replace-css-and-js-driven-animations*/}
+
+View Transitions are meant to be used for UI transitions such as navigation, expanding, opening, or re-ordering. They are not meant to replace all the animations in your app.
+
+In our example app above, notice that there are already animations when you click the "like" button and in the Suspense fallback glimmer. These are good use cases for CSS animations because they are animating a specific element.
+
+</Note>
+
+### Animating navigations {/*animating-navigations*/}
+
+Our app includes a Suspense-enabled router, with [page transitions already marked as Transitions](/reference/react/useTransition#building-a-suspense-enabled-router), which means navigations are performed with `startTransition`:
+
+```js
+function navigate(url) {
+  startTransition(() => {
+    go(url);
+  });
+}
+```
+
+`startTransition` is a View Transition trigger, so we can add `<ViewTransition>` to animate between pages:
+
+```js
+// "what" to animate
+<ViewTransition key={url}>
+  {url === '/' ? <Home /> : <TalkDetails />}
+</ViewTransition>
+```
+
+When the `url` changes, the `<ViewTransition>` and new route are rendered. Since the `<ViewTransition>` was updated inside of `startTransition`, the `<ViewTransition>` is activated for an animation.
+
+
+By default, View Transitions include the browser default cross-fade animation. Adding this to our example, we now have a cross-fade whenever we navigate between pages: 
+
+<Sandpack>
+
+```js src/App.js active
+import {unstable_ViewTransition as ViewTransition} from 'react'; import Details from './Details'; import Home from './Home'; import {useRouter} from './router';
+
+export default function App() {
+  const {url} = useRouter();
+  
+  // Use ViewTransition to animate between pages.
+  // No additional CSS needed by default.
+  return (
+    <ViewTransition>
+      {url === '/' ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    >
+      {children}
+    </div>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {useState, createContext,use,useTransition,useLayoutEffect,useEffect} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+  
+  
+  
+  
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+
+  function navigateBack(url) {
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+Since our router already updates the route using `startTransition`, this one line change to add `<ViewTransition>` activates with the default cross-fade animation. 
+
+If you're curious how this works, see the docs for [How does `<ViewTransition>` work?](/reference/react/ViewTransition#how-does-viewtransition-work)
+
+<Note>
+
+#### Opting out of `<ViewTransition>` animations {/*opting-out-of-viewtransition-animations*/}
+
+In this example, we're wrapping the root of the app in `<ViewTransition>` for simplicity, but this means that all transitions in the app will be animated, which can lead to unexpected animations. 
+
+To fix, we're wrapping route children with `"none"` so each page can control its own animation:
+
+```js
+// Layout.js
+<ViewTransition default="none">
+  {children}
+</ViewTransition>
+```
+
+In practice, navigations should be done via "enter" and "exit" props, or by using Transition Types. 
+
+</Note>
+
+### Customizing animations {/*customizing-animations*/}
+
+By default, `<ViewTransition>` includes the default cross-fade from the browser.
+
+To customize animations, you can provide props to the `<ViewTransition>` component to specify which animations to use, based on [how the `<ViewTransition>` activates](/reference/react/ViewTransition#props).
+
+For example, we can slow down the `default` cross fade animation:
+
+```js
+<ViewTransition default="slow-fade">
+  <Home />
+</ViewTransition>
+```
+
+And define `slow-fade` in CSS using [view transition classes](/reference/react/ViewTransition#view-transition-classes):
+
+```css
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+Now, the cross fade is slower:
+
+<Sandpack>
+
+```js src/App.js active
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Define a default animation of .slow-fade.
+  // See animations.css for the animation definiton.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === '/' ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    >
+      {children}
+    </div>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {
+  useState,
+  createContext,
+  use,
+  useTransition,
+  useLayoutEffect,
+  useEffect,
+} from "react";
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+export function Router({ children }) {
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  const [isPending, startTransition] = useTransition();
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  function navigateBack(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Define .slow-fade using view transition classes */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+See [Styling View Transitions](/reference/react/ViewTransition#styling-view-transitions) for a full guide on styling `<ViewTransition>`.
+
+### Shared Element Transitions {/*shared-element-transitions*/}
+
+When two pages include the same element, often you want to animate it from one page to the next.
+
+To do this you can add a unique `name` to the `<ViewTransition>`:
+
+```js
+<ViewTransition name={`video-${video.id}`}>
+  <Thumbnail video={video} />
+</ViewTransition>
+```
+
+Now the video thumbnail animates between the two pages:
+
+<Sandpack>
+
+```js src/App.js
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Keeping our default slow-fade.
+  // This allows the content not in the shared
+  // element transition to cross-fade.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {heading}
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js active
+import { useState, unstable_ViewTransition as ViewTransition } from "react"; import LikeButton from "./LikeButton"; import { useRouter } from "./router"; import { PauseIcon, PlayIcon } from "./Icons"; import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {
+  useState,
+  createContext,
+  use,
+  useTransition,
+  useLayoutEffect,
+  useEffect,
+} from "react";
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+export function Router({ children }) {
+  const [routerState, setRouterState] = useState({
+    pendingNav: () => {},
+    url: document.location.pathname,
+  });
+  const [isPending, startTransition] = useTransition();
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  function navigate(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  function navigateBack(url) {
+    // Update router state in transition.
+    startTransition(() => {
+      go(url);
+    });
+  }
+
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+By default, React automatically generates a unique `name` for each element activated for a transition (see [How does `<ViewTransition>` work](/reference/react/ViewTransition#how-does-viewtransition-work)). When React sees a transition where a `<ViewTransition>` with a `name` is removed and a new `<ViewTransition>` with the same `name` is added, it will activate a shared element transition.
+
+For more info, see the docs for [Animating a Shared Element](/reference/react/ViewTransition#animating-a-shared-element).
+
+### Animating based on cause {/*animating-based-on-cause*/}
+
+Sometimes, you may want elements to animate differently based on how it was triggered. For this use case, we've added a new API called `addTransitionType` to specify the cause of a transition:
+
+```js {4,11}
+function navigate(url) {
+  startTransition(() => {
+    // Transition type for the cause "nav forward"
+    addTransitionType('nav-forward');
+    go(url);
+  });
+}
+function navigateBack(url) {
+  startTransition(() => {
+    // Transition type for the cause "nav backward"
+    addTransitionType('nav-back');
+    go(url);
+  });
+}
+```
+
+With transition types, you can provide custom animations via props to `<ViewTransition>`. Let's add a shared element transition to the header for "6 Videos" and "Back":
+
+```js {4,5}
+<ViewTransition
+  name="nav"
+  share={{
+    'nav-forward': 'slide-forward',
+    'nav-back': 'slide-back',
+  }}>
+  {heading}
+</ViewTransition>
+```
+
+Here we pass a `share` prop to define how to animate based on the transition type. When the share transition activates from `nav-forward`, the view transition class `slide-forward` is applied. When it's from `nav-back`, the `slide-back` animation is activated. Let's define these animations in CSS:
+
+```css
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: ...
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: ...
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: ...
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: ...
+}
+```
+
+Now we can animate the header along with thumbnail based on navigation type:
+
+<Sandpack>
+
+```js src/App.js hidden
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Keeping our default slow-fade.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { use, Suspense } from "react";
+import { ChevronLeft } from "./Icons";
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={video.id} />
+        </Suspense>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js active
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* New keyframes to support our animations above. */
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Previously defined animations. */
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+### Animating Suspense Boundaries {/*animating-suspense-boundaries*/}
+
+Suspense will also activate View Transitions. 
+
+To animate the fallback to content, we can wrap `Suspense` with `<ViewTranstion>`:
+
+```js
+<ViewTransition>
+  <Suspense fallback={<VideoInfoFallback />}>
+    <VideoInfo />
+  </Suspense>
+</ViewTransition>
+```
+
+By adding this, the fallback will cross-fade into the content. Click a video and see the video info animate in:
+
+<Sandpack>
+
+```js src/App.js hidden
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Default slow-fade animation.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js active
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react"; import { fetchVideo, fetchVideoDetails } from "./data"; import { Thumbnail, VideoControls } from "./Videos"; import { useRouter } from "./router"; import Layout from "./Layout"; import { ChevronLeft } from "./Icons";
+
+function VideoDetails({ id }) {
+  // Cross-fade the fallback to content.
+  return (
+    <ViewTransition default="slow-fade">
+      <Suspense fallback={<VideoInfoFallback />}>
+          <VideoInfo id={id} />
+      </Suspense>
+    </ViewTransition>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <div>
+      <div className="fit fallback title"></div>
+      <div className="fit fallback description"></div>
+    </div>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <div>
+      <p className="fit info-title">{details.title}</p>
+      <p className="fit info-description">{details.description}</p>
+    </div>
+  );
+}
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Slide the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+/* Slide the content up */
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Define the new keyframes */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+/* Previously defined animations below */
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+We can also provide custom animations using an `exit` on the fallback, and `enter` on the content:
+
+```js {3,8}
+<Suspense
+  fallback={
+    <ViewTransition exit="slide-down">
+      <VideoInfoFallback />
+    </ViewTransition>
+  }
+>
+  <ViewTransition enter="slide-up">
+    <VideoInfo id={id} />
+  </ViewTransition>
+</Suspense>
+```
+
+Here's how we'll define `slide-down` and `slide-up` with CSS:
+
+```css {1, 6}
+::view-transition-old(.slide-down) { 
+  /* Slide the fallback down */
+  animation: ...;
+}
+
+::view-transition-new(.slide-up) {
+  /* Slide the content up */
+  animation: ...;
+}
+```
+
+Now, the Suspense content replaces the fallback with a sliding animation:
+
+<Sandpack>
+
+```js src/App.js hidden
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Default slow-fade animation.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js active
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react"; import { fetchVideo, fetchVideoDetails } from "./data"; import { Thumbnail, VideoControls } from "./Videos"; import { useRouter } from "./router"; import Layout from "./Layout"; import { ChevronLeft } from "./Icons";
+
+function VideoDetails({ id }) {
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js hidden
+import { Video } from "./Videos";
+import Layout from "./Layout";
+import { fetchVideos } from "./data";
+import { useId, useState, use } from "react";
+import { IconSearch } from "./Icons";
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState("");
+  const foundVideos = filterVideos(videos, searchText);
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <div className="video-list">
+        {foundVideos.length === 0 && (
+          <div className="no-results">No results</div>
+        )}
+        <div className="videos">
+          {foundVideos.map((video) => (
+            <Video key={video.id} video={video} />
+          ))}
+        </div>
+      </div>
+    </Layout>
+  );
+}
+
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Slide the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+/* Slide the content up */
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Define the new keyframes */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+/* Previously defined animations below */
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+
+### Animating Lists {/*animating-lists*/}
+
+You can also use `<ViewTransition>` to animate lists of items as they re-order, like in a searchable list of items:
+
+```js {3,5}
+<div className="videos">
+  {filteredVideos.map((video) => (
+    <ViewTransition key={video.id}>
+      <Video video={video} />
+    </ViewTransition>
+  ))}
+</div>
+```
+
+To activate the ViewTransition, we can use `useDeferredValue`:
+
+```js {2}
+const [searchText, setSearchText] = useState('');
+const deferredSearchText = useDeferredValue(searchText);
+const filteredVideos = filterVideos(videos, deferredSearchText);
+```
+
+Now the items animate as you type in the search bar:
+
+<Sandpack>
+
+```js src/App.js hidden
+import { unstable_ViewTransition as ViewTransition } from "react";
+import Details from "./Details";
+import Home from "./Home";
+import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+
+  // Default slow-fade animation.
+  return (
+    <ViewTransition default="slow-fade">
+      {url === "/" ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react";
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+
+/* Slide animation for Suspense */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+### Final result {/*final-result*/}
+
+By adding a few `<ViewTransition>` components and a few lines of CSS, we were able to add all the animations above into the final result.
+
+We're excited about View Transitions and think they will level up the apps you're able to build. They're ready to start trying today in the experimental channel of React releases.
+
+Let's remove the slow fade, and take a look at the final result:
+
+<Sandpack>
+
+```js src/App.js
+import {unstable_ViewTransition as ViewTransition} from 'react'; import Details from './Details'; import Home from './Home'; import {useRouter} from './router';
+
+export default function App() {
+  const {url} = useRouter();
+
+  // Animate with a cross fade between pages.
+  return (
+    <ViewTransition key={url}>
+      {url === '/' ? <Home /> : <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react"; import { fetchVideo, fetchVideoDetails } from "./data"; import { Thumbnail, VideoControls } from "./Videos"; import { useRouter } from "./router"; import Layout from "./Layout"; import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js
+import { useState, unstable_ViewTransition as ViewTransition } from "react"; import LikeButton from "./LikeButton"; import { useRouter } from "./router"; import { PauseIcon, PlayIcon } from "./Icons"; import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* Slide animations for Suspense the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+If you're curious to know more about how they work, check out [How Does `<ViewTransition>` Work](/reference/react/ViewTransition#how-does-viewtransition-work) in the docs.
+
+_For more background on how we built View Transitions, see: [#31975](https://github.com/facebook/react/pull/31975), [#32105](https://github.com/facebook/react/pull/32105), [#32041](https://github.com/facebook/react/pull/32041), [#32734](https://github.com/facebook/react/pull/32734), [#32797](https://github.com/facebook/react/pull/32797) [#31999](https://github.com/facebook/react/pull/31999), [#32031](https://github.com/facebook/react/pull/32031), [#32050](https://github.com/facebook/react/pull/32050), [#32820](https://github.com/facebook/react/pull/32820), [#32029](https://github.com/facebook/react/pull/32029), [#32028](https://github.com/facebook/react/pull/32028), and [#32038](https://github.com/facebook/react/pull/32038) by [@sebmarkbage](https://twitter.com/sebmarkbage) (thanks Seb!)._
+
+---
+
+## Activity {/*activity*/}
+
+In [past](/blog/2022/06/15/react-labs-what-we-have-been-working-on-june-2022#offscreen) [updates](/blog/2024/02/15/react-labs-what-we-have-been-working-on-february-2024#offscreen-renamed-to-activity), we shared that we were researching an API to allow components to be visually hidden and deprioritized, preserving UI state with reduced performance costs relative to unmounting or hiding with CSS.
+
+We're now ready to share the API and how it works, so you can start testing it in experimental React versions.
+
+`<Activity>` is a new component to hide and show parts of the UI:
+
+```js [[1, 1, "'visible'"], [2, 1, "'hidden'"]]
+<Activity mode={isVisible ? 'visible' : 'hidden'}>
+  <Page />
+</Activity>
+```
+
+When an Activity is <CodeStep step={1}>visible</CodeStep> it's rendered as normal. When an Activity is <CodeStep step={2}>hidden</CodeStep> it is unmounted, but will save its state and continue to render at a lower priority than anything visible on screen.
+
+You can use `Activity` to save state for parts of the UI the user isn't using, or pre-render parts that a user is likely to use next.
+
+Let's look at some examples improving the View Transition examples above.
+
+<Note>
+
+**Effects don’t mount when an Activity is hidden.**
+
+When an `<Activity>` is `hidden`, Effects are unmounted. Conceptually, the component is unmounted, but React saves the state for later.
+
+In practice, this works as expected if you have followed the [You Might Not Need an Effect](/learn/you-might-not-need-an-effect) guide. To eagerly find problematic Effects, we recommend adding [`<StrictMode>`](/reference/react/StrictMode) which will eagerly perform Activity unmounts and mounts to catch any unexpected side effects.
+
+</Note>
+
+### Restoring state with Activity {/*restoring-state-with-activity*/}
+
+When a user navigates away from a page, it's common to stop rendering the old page:
+
+```js {6,7}
+function App() {
+  const { url } = useRouter();
+  
+  return (
+    <>
+      {url === '/' && <Home />}
+      {url !== '/' && <Details />}
+    </>
+  );
+}
+```
+
+However, this means if the user goes back to the old page, all of the previous state is lost. For example, if the `<Home />` page has an `<input>` field, when the user leaves the page the `<input>` is unmounted, and all of the text they had typed is lost.
+
+Activity allows you to keep the state around as the user changes pages, so when they come back they can resume where they left off. This is done by wrapping part of the tree in `<Activity>` and toggling the `mode`:
+
+```js {6-8}
+function App() {
+  const { url } = useRouter();
+  
+  return (
+    <>
+      <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+        <Home />
+      </Activity>
+      {url !== '/' && <Details />}
+    </>
+  );
+}
+```
+
+With this change, we can improve on our View Transitions example above. Before, when you searched for a video, selected one, and returned, your search filter was lost. With Activity, your search filter is restored and you can pick up where you left off.
+
+Try searching for a video, selecting it, and clicking "back":
+
+<Sandpack>
+
+```js src/App.js
+import { unstable_ViewTransition as ViewTransition, unstable_Activity as Activity } from "react"; import Details from "./Details"; import Home from "./Home"; import { useRouter } from "./router";
+
+export default function App() {
+  const { url } = useRouter();
+  
+  return (
+    // View Transitions know about Activity
+    <ViewTransition>
+      {/* Render Home in Activity so we don't lose state */}
+      <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+        <Home />
+      </Activity>
+      {url !== '/' && <Details />}
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js hidden
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react";
+import { fetchVideo, fetchVideoDetails } from "./data";
+import { Thumbnail, VideoControls } from "./Videos";
+import { useRouter } from "./router";
+import Layout from "./Layout";
+import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details() {
+  const { url, navigateBack } = useRouter();
+  const videoId = url.split("/").pop();
+  const video = use(fetchVideo(videoId));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js hidden
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+
+/* Slide animations for Suspense the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+### Pre-rendering with Activity {/*prerender-with-activity*/}
+
+Sometimes, you may want to prepare the next part of the UI a user is likely to use ahead of time, so it's ready by the time they are ready to use it. This is especially useful if the next route needs to suspend on data it needs to render, because you can help ensure the data is already fetched before the user navigates.
+
+For example, our app currently needs to suspend to load the data for each video when you select one. We can improve this by rendering all of the pages in a hidden `<Activity>` until the user navigates:
+
+```js {2,5,8}
+<ViewTransition>
+  <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+    <Home />
+  </Activity>
+  <Activity mode={url === '/details/1' ? 'visible' : 'hidden'}>
+    <Details id={id} />
+  </Activity>
+  <Activity mode={url === '/details/1' ? 'visible' : 'hidden'}>
+    <Details id={id} />
+  </Activity>
+<ViewTransition>
+```
+
+With this update, if the content on the next page has time to pre-render, it will animate in without the Suspense fallback. Click a video, and notice that the video title and description on the Details page render immediately, without a fallback:
+
+<Sandpack>
+
+```js src/App.js
+import { unstable_ViewTransition as ViewTransition, unstable_Activity as Activity, use } from "react"; import Details from "./Details"; import Home from "./Home"; import { useRouter } from "./router"; import {fetchVideos} from './data'
+
+export default function App() {
+  const { url } = useRouter();
+  const videoId = url.split("/").pop();
+  const videos = use(fetchVideos());
+  
+  return (
+    <ViewTransition>
+      {/* Render videos in Activity to pre-render them */}
+      {videos.map(({id}) => (
+        <Activity key={id} mode={videoId === id ? 'visible' : 'hidden'}>
+          <Details id={id}/>
+        </Activity>
+      ))}
+      <Activity mode={url === '/' ? 'visible' : 'hidden'}>
+        <Home />
+      </Activity>
+    </ViewTransition>
+  );
+}
+```
+
+```js src/Details.js
+import { use, Suspense, unstable_ViewTransition as ViewTransition } from "react"; import { fetchVideo, fetchVideoDetails } from "./data"; import { Thumbnail, VideoControls } from "./Videos"; import { useRouter } from "./router"; import Layout from "./Layout"; import { ChevronLeft } from "./Icons";
+
+function VideoDetails({id}) {
+  // Animate from Suspense fallback to content.
+  // If this is pre-rendered then the fallback
+  // won't need to show.
+  return (
+    <Suspense
+      fallback={
+        // Animate the fallback down.
+        <ViewTransition exit="slide-down">
+          <VideoInfoFallback />
+        </ViewTransition>
+      }
+    >
+      {/* Animate the content up */}
+      <ViewTransition enter="slide-up">
+        <VideoInfo id={id} />
+      </ViewTransition>
+    </Suspense>
+  );
+}
+
+function VideoInfoFallback() {
+  return (
+    <>
+      <div className="fallback title"></div>
+      <div className="fallback description"></div>
+    </>
+  );
+}
+
+export default function Details({id}) {
+  const { url, navigateBack } = useRouter();
+  const video = use(fetchVideo(id));
+
+  return (
+    <Layout
+      heading={
+        <div
+          className="fit back"
+          onClick={() => {
+            navigateBack("/");
+          }}
+        >
+          <ChevronLeft /> Back
+        </div>
+      }
+    >
+      <div className="details">
+        <Thumbnail video={video} large>
+          <VideoControls />
+        </Thumbnail>
+        <VideoDetails id={video.id} />
+      </div>
+    </Layout>
+  );
+}
+
+function VideoInfo({ id }) {
+  const details = use(fetchVideoDetails(id));
+  return (
+    <>
+      <p className="info-title">{details.title}</p>
+      <p className="info-description">{details.description}</p>
+    </>
+  );
+}
+```
+
+```js src/Home.js hidden
+import { useId, useState, use, useDeferredValue, unstable_ViewTransition as ViewTransition } from "react";import { Video } from "./Videos";import Layout from "./Layout";import { fetchVideos } from "./data";import { IconSearch } from "./Icons";
+
+function SearchList({searchText, videos}) {
+  // Activate with useDeferredValue ("when") 
+  const deferredSearchText = useDeferredValue(searchText);
+  const filteredVideos = filterVideos(videos, deferredSearchText);
+  return (
+    <div className="video-list">
+      {filteredVideos.length === 0 && (
+        <div className="no-results">No results</div>
+      )}
+      <div className="videos">
+        {filteredVideos.map((video) => (
+          // Animate each item in list ("what") 
+          <ViewTransition key={video.id}>
+            <Video video={video} />
+          </ViewTransition>
+        ))}
+      </div>
+    </div>
+  );
+}
+
+export default function Home() {
+  const videos = use(fetchVideos());
+  const count = videos.length;
+  const [searchText, setSearchText] = useState('');
+  
+  return (
+    <Layout heading={<div className="fit">{count} Videos</div>}>
+      <SearchInput value={searchText} onChange={setSearchText} />
+      <SearchList videos={videos} searchText={searchText} />
+    </Layout>
+  );
+}
+
+function SearchInput({ value, onChange }) {
+  const id = useId();
+  return (
+    <form className="search" onSubmit={(e) => e.preventDefault()}>
+      <label htmlFor={id} className="sr-only">
+        Search
+      </label>
+      <div className="search-input">
+        <div className="search-icon">
+          <IconSearch />
+        </div>
+        <input
+          type="text"
+          id={id}
+          placeholder="Search"
+          value={value}
+          onChange={(e) => onChange(e.target.value)}
+        />
+      </div>
+    </form>
+  );
+}
+
+function filterVideos(videos, query) {
+  const keywords = query
+    .toLowerCase()
+    .split(" ")
+    .filter((s) => s !== "");
+  if (keywords.length === 0) {
+    return videos;
+  }
+  return videos.filter((video) => {
+    const words = (video.title + " " + video.description)
+      .toLowerCase()
+      .split(" ");
+    return keywords.every((kw) => words.some((w) => w.includes(kw)));
+  });
+}
+```
+
+```js src/Icons.js hidden
+export function ChevronLeft() {
+  return (
+    <svg
+      className="chevron-left"
+      xmlns="http://www.w3.org/2000/svg"
+      width="20"
+      height="20"
+      viewBox="0 0 20 20">
+      <g fill="none" fillRule="evenodd" transform="translate(-446 -398)">
+        <path
+          fill="currentColor"
+          fillRule="nonzero"
+          d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z"
+          transform="translate(356.5 164.5)"
+        />
+        <polygon points="446 418 466 418 466 398 446 398" />
+      </g>
+    </svg>
+  );
+}
+
+export function PauseIcon() {
+  return (
+    <svg
+      className="control-icon"
+      style={{padding: '4px'}}
+      width="100"
+      height="100"
+      viewBox="0 0 512 512"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M256 0C114.617 0 0 114.615 0 256s114.617 256 256 256 256-114.615 256-256S397.383 0 256 0zm-32 320c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128zm128 0c0 8.836-7.164 16-16 16h-32c-8.836 0-16-7.164-16-16V192c0-8.836 7.164-16 16-16h32c8.836 0 16 7.164 16 16v128z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+
+export function PlayIcon() {
+  return (
+    <svg
+      className="control-icon"
+      width="100"
+      height="100"
+      viewBox="0 0 72 72"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg">
+      <path
+        fillRule="evenodd"
+        clipRule="evenodd"
+        d="M36 69C54.2254 69 69 54.2254 69 36C69 17.7746 54.2254 3 36 3C17.7746 3 3 17.7746 3 36C3 54.2254 17.7746 69 36 69ZM52.1716 38.6337L28.4366 51.5801C26.4374 52.6705 24 51.2235 24 48.9464V23.0536C24 20.7764 26.4374 19.3295 28.4366 20.4199L52.1716 33.3663C54.2562 34.5034 54.2562 37.4966 52.1716 38.6337Z"
+        fill="currentColor"
+      />
+    </svg>
+  );
+}
+export function Heart({liked, animate}) {
+  return (
+    <>
+      <svg
+        className="absolute overflow-visible"
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        <circle
+          className={`circle ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+          cx="12"
+          cy="12"
+          r="11.5"
+          fill="transparent"
+          strokeWidth="0"
+          stroke="currentColor"
+        />
+      </svg>
+
+      <svg
+        className={`heart ${liked ? 'liked' : ''} ${animate ? 'animate' : ''}`}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg">
+        {liked ? (
+          <path
+            d="M12 23a.496.496 0 0 1-.26-.074C7.023 19.973 0 13.743 0 8.68c0-4.12 2.322-6.677 6.058-6.677 2.572 0 5.108 2.387 5.134 2.41l.808.771.808-.771C12.834 4.387 15.367 2 17.935 2 21.678 2 24 4.558 24 8.677c0 5.06-7.022 11.293-11.74 14.246a.496.496 0 0 1-.26.074V23z"
+            fill="currentColor"
+          />
+        ) : (
+          <path
+            fillRule="evenodd"
+            clipRule="evenodd"
+            d="m12 5.184-.808-.771-.004-.004C11.065 4.299 8.522 2.003 6 2.003c-3.736 0-6 2.558-6 6.677 0 4.47 5.471 9.848 10 13.079.602.43 1.187.82 1.74 1.167A.497.497 0 0 0 12 23v-.003c.09 0 .182-.026.26-.074C16.977 19.97 24 13.737 24 8.677 24 4.557 21.743 2 18 2c-2.569 0-5.166 2.387-5.192 2.413L12 5.184zm-.002 15.525c2.071-1.388 4.477-3.342 6.427-5.47C20.72 12.733 22 10.401 22 8.677c0-1.708-.466-2.855-1.087-3.55C20.316 4.459 19.392 4 18 4c-.726 0-1.63.364-2.5.9-.67.412-1.148.82-1.266.92-.03.025-.037.031-.019.014l-.013.013L12 7.949 9.832 5.88a10.08 10.08 0 0 0-1.33-.977C7.633 4.367 6.728 4.003 6 4.003c-1.388 0-2.312.459-2.91 1.128C2.466 5.826 2 6.974 2 8.68c0 1.726 1.28 4.058 3.575 6.563 1.948 2.127 4.352 4.078 6.423 5.466z"
+            fill="currentColor"
+          />
+        )}
+      </svg>
+    </>
+  );
+}
+
+export function IconSearch(props) {
+  return (
+    <svg width="1em" height="1em" viewBox="0 0 20 20">
+      <path
+        d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z"
+        stroke="currentColor"
+        fill="none"
+        strokeWidth="2"
+        fillRule="evenodd"
+        strokeLinecap="round"
+        strokeLinejoin="round"></path>
+    </svg>
+  );
+}
+```
+
+```js src/Layout.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react'; import { useIsNavPending } from "./router";
+
+export default function Page({ heading, children }) {
+  const isPending = useIsNavPending();
+  return (
+    <div className="page">
+      <div className="top">
+        <div className="top-nav">
+          {/* Custom classes based on transition type. */}
+          <ViewTransition
+            name="nav"
+            share={{
+              'nav-forward': 'slide-forward',
+              'nav-back': 'slide-back',
+            }}>
+            {heading}
+          </ViewTransition>
+          {isPending && <span className="loader"></span>}
+        </div>
+      </div>
+      {/* Opt-out of ViewTransition for the content. */}
+      {/* Content can define it's own ViewTransition. */}
+      <ViewTransition default="none">
+        <div className="bottom">
+          <div className="content">{children}</div>
+        </div>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+```js src/LikeButton.js hidden
+import {useState} from 'react';
+import {Heart} from './Icons';
+
+// A hack since we don't actually have a backend.
+// Unlike local state, this survives videos being filtered.
+const likedVideos = new Set();
+
+export default function LikeButton({video}) {
+  const [isLiked, setIsLiked] = useState(() => likedVideos.has(video.id));
+  const [animate, setAnimate] = useState(false);
+  return (
+    <button
+      className={`like-button ${isLiked && 'liked'}`}
+      aria-label={isLiked ? 'Unsave' : 'Save'}
+      onClick={() => {
+        const nextIsLiked = !isLiked;
+        if (nextIsLiked) {
+          likedVideos.add(video.id);
+        } else {
+          likedVideos.delete(video.id);
+        }
+        setAnimate(true);
+        setIsLiked(nextIsLiked);
+      }}>
+      <Heart liked={isLiked} animate={animate} />
+    </button>
+  );
+}
+```
+
+```js src/Videos.js hidden
+import { useState, unstable_ViewTransition as ViewTransition } from "react";
+import LikeButton from "./LikeButton";
+import { useRouter } from "./router";
+import { PauseIcon, PlayIcon } from "./Icons";
+import { startTransition } from "react";
+
+export function Thumbnail({ video, children }) {
+  // Add a name to animate with a shared element transition.
+  // This uses the default animation, no additional css needed.
+  return (
+    <ViewTransition name={`video-${video.id}`}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      >
+        {children}
+      </div>
+    </ViewTransition>
+  );
+}
+
+export function VideoControls() {
+  const [isPlaying, setIsPlaying] = useState(false);
+
+  return (
+    <span
+      className="controls"
+      onClick={() =>
+        startTransition(() => {
+          setIsPlaying((p) => !p);
+        })
+      }
+    >
+      {isPlaying ? <PauseIcon /> : <PlayIcon />}
+    </span>
+  );
+}
+
+export function Video({ video }) {
+  const { navigate } = useRouter();
+
+  return (
+    <div className="video">
+      <div
+        className="link"
+        onClick={(e) => {
+          e.preventDefault();
+          navigate(`/video/${video.id}`);
+        }}
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+      <LikeButton video={video} />
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+const videos = [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  },
+  {
+    id: '5',
+    title: 'Fifth video',
+    description: 'Video description',
+    image: 'yellow',
+  },
+  {
+    id: '6',
+    title: 'Sixth video',
+    description: 'Video description',
+    image: 'gray',
+  },
+];
+
+let videosCache = new Map();
+let videoCache = new Map();
+let videoDetailsCache = new Map();
+const VIDEO_DELAY = 1;
+const VIDEO_DETAILS_DELAY = 1000;
+export function fetchVideos() {
+  if (videosCache.has(0)) {
+    return videosCache.get(0);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos);
+    }, VIDEO_DELAY);
+  });
+  videosCache.set(0, promise);
+  return promise;
+}
+
+export function fetchVideo(id) {
+  if (videoCache.has(id)) {
+    return videoCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DELAY);
+  });
+  videoCache.set(id, promise);
+  return promise;
+}
+
+export function fetchVideoDetails(id) {
+  if (videoDetailsCache.has(id)) {
+    return videoDetailsCache.get(id);
+  }
+  const promise = new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(videos.find((video) => video.id === id));
+    }, VIDEO_DETAILS_DELAY);
+  });
+  videoDetailsCache.set(id, promise);
+  return promise;
+}
+```
+
+```js src/router.js hidden
+import {useState, createContext, use, useTransition, useLayoutEffect, useEffect, unstable_addTransitionType as addTransitionType} from "react";
+
+export function Router({ children }) {
+  const [isPending, startTransition] = useTransition();
+  const [routerState, setRouterState] = useState({pendingNav: () => {}, url: document.location.pathname});
+  function navigate(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav forward"
+      addTransitionType('nav-forward');
+      go(url);
+    });
+  }
+  function navigateBack(url) {
+    startTransition(() => {
+      // Transition type for the cause "nav backward"
+      addTransitionType('nav-back');
+      go(url);
+    });
+  }
+
+  function go(url) {
+    setRouterState({
+      url,
+      pendingNav() {
+        window.history.pushState({}, "", url);
+      },
+    });
+  }
+  
+  useEffect(() => {
+    function handlePopState() {
+      // This should not animate because restoration has to be synchronous.
+      // Even though it's a transition.
+      startTransition(() => {
+        setRouterState({
+          url: document.location.pathname + document.location.search,
+          pendingNav() {
+            // Noop. URL has already updated.
+          },
+        });
+      });
+    }
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, []);
+  const pendingNav = routerState.pendingNav;
+  useLayoutEffect(() => {
+    pendingNav();
+  }, [pendingNav]);
+
+  return (
+    <RouterContext
+      value={{
+        url: routerState.url,
+        navigate,
+        navigateBack,
+        isPending,
+        params: {},
+      }}
+    >
+      {children}
+    </RouterContext>
+  );
+}
+
+const RouterContext = createContext({ url: "/", params: {} });
+
+export function useRouter() {
+  return use(RouterContext);
+}
+
+export function useIsNavPending() {
+  return use(RouterContext).isPending;
+}
+
+```
+
+```css src/styles.css hidden
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Rg.woff2) format("woff2");
+  font-weight: 400;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Md.woff2) format("woff2");
+  font-weight: 500;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 600;
+  font-style: normal;
+  font-display: swap;
+}
+
+@font-face {
+  font-family: Optimistic Text;
+  src: url(https://react.dev/fonts/Optimistic_Text_W_Bd.woff2) format("woff2");
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
+* {
+  box-sizing: border-box;
+}
+
+html {
+  background-image: url(https://react.dev/images/meta-gradient-dark.png);
+  background-size: 100%;
+  background-position: -100%;
+  background-color: rgb(64 71 86);
+  background-repeat: no-repeat;
+  height: 100%;
+  width: 100%;
+}
+
+body {
+  font-family: Optimistic Text, -apple-system, ui-sans-serif, system-ui, sans-serif, Apple Color Emoji, Segoe UI Emoji, Segoe UI Symbol, Noto Color Emoji;
+  padding: 10px 0 10px 0;
+  margin: 0;
+  display: flex;
+  justify-content: center;
+}
+
+#root {
+  flex: 1 1;
+  height: auto;
+  background-color: #fff;
+  border-radius: 10px;
+  max-width: 450px;
+  min-height: 600px;
+  padding-bottom: 10px;
+}
+
+h1 {
+  margin-top: 0;
+  font-size: 22px;
+}
+
+h2 {
+  margin-top: 0;
+  font-size: 20px;
+}
+
+h3 {
+  margin-top: 0;
+  font-size: 18px;
+}
+
+h4 {
+  margin-top: 0;
+  font-size: 16px;
+}
+
+h5 {
+  margin-top: 0;
+  font-size: 14px;
+}
+
+h6 {
+  margin-top: 0;
+  font-size: 12px;
+}
+
+code {
+  font-size: 1.2em;
+}
+
+ul {
+  padding-inline-start: 20px;
+}
+
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}
+
+.absolute {
+  position: absolute;
+}
+
+.overflow-visible {
+  overflow: visible;
+}
+
+.visible {
+  overflow: visible;
+}
+
+.fit {
+  width: fit-content;
+}
+
+
+/* Layout */
+.page {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.top-hero {
+  height: 200px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-image: conic-gradient(
+      from 90deg at -10% 100%,
+      #2b303b 0deg,
+      #2b303b 90deg,
+      #16181d 1turn
+  );
+}
+
+.bottom {
+  flex: 1;
+  overflow: auto;
+}
+
+.top-nav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 0;
+  padding: 0 12px;
+  top: 0;
+  width: 100%;
+  height: 44px;
+  color: #23272f;
+  font-weight: 700;
+  font-size: 20px;
+  z-index: 100;
+  cursor: default;
+}
+
+.content {
+  padding: 0 12px;
+  margin-top: 4px;
+}
+
+
+.loader {
+  color: #23272f;
+  font-size: 3px;
+  width: 1em;
+  margin-right: 18px;
+  height: 1em;
+  border-radius: 50%;
+  position: relative;
+  text-indent: -9999em;
+  animation: loading-spinner 1.3s infinite linear;
+  animation-delay: 200ms;
+  transform: translateZ(0);
+}
+
+@keyframes loading-spinner {
+  0%,
+  100% {
+    box-shadow: 0 -3em 0 0.2em,
+    2em -2em 0 0em, 3em 0 0 -1em,
+    2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 0;
+  }
+  12.5% {
+    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em,
+    3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  25% {
+    box-shadow: 0 -3em 0 -0.5em,
+    2em -2em 0 0, 3em 0 0 0.2em,
+    2em 2em 0 0, 0 3em 0 -1em,
+    -2em 2em 0 -1em, -3em 0 0 -1em,
+    -2em -2em 0 -1em;
+  }
+  37.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em,
+    -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  50% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em,
+    -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
+  }
+  62.5% {
+    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0,
+    -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
+  }
+  75% {
+    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em,
+    3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
+  }
+  87.5% {
+    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em,
+    3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em,
+    -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
+  }
+}
+
+/* LikeButton */
+.like-button {
+  outline-offset: 2px;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 2.5rem;
+  height: 2.5rem;
+  cursor: pointer;
+  border-radius: 9999px;
+  border: none;
+  outline: none 2px;
+  color: #5e687e;
+  background: none;
+}
+
+.like-button:focus {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+}
+
+.like-button:active {
+  color: #a6423a;
+  background-color: rgba(166, 66, 58, .05);
+  transform: scaleX(0.95) scaleY(0.95);
+}
+
+.like-button:hover {
+  background-color: #f6f7f9;
+}
+
+.like-button.liked {
+  color: #a6423a;
+}
+
+/* Icons */
+@keyframes circle {
+  0% {
+    transform: scale(0);
+    stroke-width: 16px;
+  }
+
+  50% {
+    transform: scale(.5);
+    stroke-width: 16px;
+  }
+
+  to {
+    transform: scale(1);
+    stroke-width: 0;
+  }
+}
+
+.circle {
+  color: rgba(166, 66, 58, .5);
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4,0,.2,1);
+}
+
+.circle.liked.animate {
+  animation: circle .3s forwards;
+}
+
+.heart {
+  width: 1.5rem;
+  height: 1.5rem;
+}
+
+.heart.liked {
+  transform-origin: center;
+  transition-property: all;
+  transition-duration: .15s;
+  transition-timing-function: cubic-bezier(.4, 0, .2, 1);
+}
+
+.heart.liked.animate {
+  animation: scale .35s ease-in-out forwards;
+}
+
+.control-icon {
+  color: hsla(0, 0%, 100%, .5);
+  filter:  drop-shadow(0 20px 13px rgba(0, 0, 0, .03)) drop-shadow(0 8px 5px rgba(0, 0, 0, .08));
+}
+
+.chevron-left {
+  margin-top: 2px;
+  rotate: 90deg;
+}
+
+
+/* Video */
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+
+.thumbnail.yellow {
+  background-image: conic-gradient(at top right, #c76a15, #FABD62, #2b3491);
+}
+
+.thumbnail.gray {
+  background-image: conic-gradient(at top right, #c76a15, #4E5769, #2b3491);
+}
+
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+}
+
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+
+.video .info:hover {
+  text-decoration: underline;
+}
+
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+
+/* Details */
+.details .thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 100%;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+
+.video-details-title {
+  margin-top: 8px;
+}
+
+.video-details-speaker {
+  display: flex;
+  gap: 8px;
+  margin-top: 10px
+}
+
+.back {
+  display: flex;
+  align-items: center;
+  margin-left: -5px;
+  cursor: pointer;
+}
+
+.back:hover {
+  text-decoration: underline;
+}
+
+.info-title {
+  font-size: 1.5rem;
+  font-weight: 700;
+  line-height: 1.25;
+  margin: 8px 0 0 0 ;
+}
+
+.info-description {
+  margin: 8px 0 0 0;
+}
+
+.controls {
+  cursor: pointer;
+}
+
+.fallback {
+  background: #f6f7f8 linear-gradient(to right, #e6e6e6 5%, #cccccc 25%, #e6e6e6 35%) no-repeat;
+  background-size: 800px 104px;
+  display: block;
+  line-height: 1.25;
+  margin: 8px 0 0 0;
+  border-radius: 5px;
+  overflow: hidden;
+
+  animation: 1s linear 1s infinite shimmer;
+  animation-delay: 300ms;
+  animation-duration: 1s;
+  animation-fill-mode: forwards;
+  animation-iteration-count: infinite;
+  animation-name: shimmer;
+  animation-timing-function: linear;
+}
+
+
+.fallback.title {
+  width: 130px;
+  height: 30px;
+
+}
+
+.fallback.description {
+  width: 150px;
+  height: 21px;
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -468px 0;
+  }
+
+  100% {
+    background-position: 468px 0;
+  }
+}
+
+.search {
+  margin-bottom: 10px;
+}
+.search-input {
+  width: 100%;
+  position: relative;
+}
+
+.search-icon {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  inset-inline-start: 0;
+  display: flex;
+  align-items: center;
+  padding-inline-start: 1rem;
+  pointer-events: none;
+  color: #99a1b3;
+}
+
+.search-input input {
+  display: flex;
+  padding-inline-start: 2.75rem;
+  padding-top: 10px;
+  padding-bottom: 10px;
+  width: 100%;
+  text-align: start;
+  background-color: rgb(235 236 240);
+  outline: 2px solid transparent;
+  cursor: pointer;
+  border: none;
+  align-items: center;
+  color: rgb(35 39 47);
+  border-radius: 9999px;
+  vertical-align: middle;
+  font-size: 15px;
+}
+
+.search-input input:hover, .search-input input:active {
+  background-color: rgb(235 236 240/ 0.8);
+  color: rgb(35 39 47/ 0.8);
+}
+
+/* Home */
+.video-list {
+  position: relative;
+}
+
+.video-list .videos {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  overflow-y: auto;
+  height: 100%;
+}
+```
+
+
+```css src/animations.css
+/* No additional animations needed */
+
+
+
+
+
+
+
+
+
+/* Previously defined animations below */
+
+
+
+
+
+
+/* Slide animations for Suspense the fallback down */
+::view-transition-old(.slide-down) {
+    animation: 150ms ease-out both fade-out, 150ms ease-out both slide-down;
+}
+
+::view-transition-new(.slide-up) {
+    animation: 210ms ease-in 150ms both fade-in, 400ms ease-in both slide-up;
+}
+
+/* Animations for view transition classed added by transition type */
+::view-transition-old(.slide-forward) {
+    /* when sliding forward, the "old" page should slide out to left. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-left;
+}
+
+::view-transition-new(.slide-forward) {
+    /* when sliding forward, the "new" page should slide in from right. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-right;
+}
+
+::view-transition-old(.slide-back) {
+    /* when sliding back, the "old" page should slide out to right. */
+    animation: 150ms cubic-bezier(0.4, 0, 1, 1) both fade-out,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-to-right;
+}
+
+::view-transition-new(.slide-back) {
+    /* when sliding back, the "new" page should slide in from left. */
+    animation: 210ms cubic-bezier(0, 0, 0.2, 1) 150ms both fade-in,
+    400ms cubic-bezier(0.4, 0, 0.2, 1) both slide-from-left;
+}
+
+/* Keyframes to support our animations above. */
+@keyframes slide-up {
+    from {
+        transform: translateY(10px);
+    }
+    to {
+        transform: translateY(0);
+    }
+}
+
+@keyframes slide-down {
+    from {
+        transform: translateY(0);
+    }
+    to {
+        transform: translateY(10px);
+    }
+}
+
+@keyframes fade-in {
+    from {
+        opacity: 0;
+    }
+}
+
+@keyframes fade-out {
+    to {
+        opacity: 0;
+    }
+}
+
+@keyframes slide-to-right {
+    to {
+        transform: translateX(50px);
+    }
+}
+
+@keyframes slide-from-right {
+    from {
+        transform: translateX(50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+@keyframes slide-to-left {
+    to {
+        transform: translateX(-50px);
+    }
+}
+
+@keyframes slide-from-left {
+    from {
+        transform: translateX(-50px);
+    }
+    to {
+        transform: translateX(0);
+    }
+}
+
+/* Default .slow-fade. */
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+```js src/index.js hidden
+import React, {StrictMode} from 'react';
+import {createRoot} from 'react-dom/client';
+import './styles.css';
+import './animations.css';
+
+import App from './App';
+import {Router} from './router';
+
+const root = createRoot(document.getElementById('root'));
+root.render(
+  <StrictMode>
+    <Router>
+      <App />
+    </Router>
+  </StrictMode>
+);
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+### Server-Side Rendering with Activity {/*server-side-rendering-with-activity*/}
+
+When using Activity on a page that uses server-side rendering (SSR), there are additional optimizations.
+
+If part of the page is rendered with `mode="hidden"`, then it will not be included in the SSR response. Instead, React will schedule a client render for the content inside Activity while the rest of the page hydrates, prioritizing the visible content on screen.
+
+For parts of the UI rendered with `mode="visible"`, React will de-prioritize hydration of content within Activity, similar to how Suspense content is hydrated at a lower priority. If the user interacts with the page, we'll prioritize hydration within the boundary if needed.
+
+These are advanced use cases, but they show the additional benefits considered with Activity.
+
+### Future modes for Activity {/*future-modes-for-activity*/}
+
+In the future, we may add more modes to Activity.
+
+For example, a common use case is rendering a modal, where the previous "inactive" page is visible behind the "active" modal view. The "hidden" mode does not work for this use case because it's not visible and not included in SSR.
+
+Instead, we're considering a new mode that would keep the content visible&mdash;and included in SSR&mdash;but keep it unmounted and de-prioritize updates. This mode may also need to "pause" DOM updates, since it can be distracting to see backgrounded content updating while a modal is open.
+
+Another mode we're considering for Activity is the ability to automatically destroy state for hidden Activities if there is too much memory being used. Since the component is already unmounted, it may be preferable to destroy state for the least recently used hidden parts of the app rather than consume too many resources.
+
+These are areas we're still exploring, and we'll share more as we make progress. For more information on what Activity includes today, [check out the docs](/reference/react/Activity).
+
+---
+
+# Features in development {/*features-in-development*/}
+
+We're also developing features to help solve the common problems below. 
+
+As we iterate on possible solutions, you may see some potential APIs we're testing being shared based on the PRs we are landing. Please keep in mind that as we try different ideas, we often change or remove different solutions after trying them out. 
+
+When the solutions we're working on are shared too early, it can create churn and confusion in the community. To balance being transparent and limiting confusion, we're sharing the problems we're currently developing solutions for, without sharing a particular solution we have in mind. 
+
+As these features progress, we'll announce them on the blog with docs included so you can try them out. 
+
+## React Performance Tracks {/*react-performance-tracks*/}
+
+We're working on a new set of custom tracks to performance profilers using browser APIs that [allow adding custom tracks](https://developer.chrome.com/docs/devtools/performance/extension) to provide more information about the performance of your React app.
+
+This feature is still in progress, so we're not ready to publish docs to fully release it as an experimental feature yet. You can get a sneak preview when using an experimental version of React, which will automatically add the performance tracks to profiles:
+
+<div style={{display: 'flex', justifyContent: 'center', marginBottom: '1rem'}}>
+  <picture >
+      <source srcset="/images/blog/react-labs-april-2025/perf_tracks.png" />
+      <img className="w-full light-image" src="/images/blog/react-labs-april-2025/perf_tracks.webp" />
+  </picture>
+  <picture >
+      <source srcset="/images/blog/react-labs-april-2025/perf_tracks_dark.png" />
+      <img className="w-full dark-image" src="/images/blog/react-labs-april-2025/perf_tracks_dark.webp" />
+  </picture>
+</div>
+
+There are a few known issues we plan to address such as performance, and the scheduler track not always "connecting" work across Suspended trees, so it's not quite ready to try. We're also still collecting feedback from early adopters to improve the design and usability of the tracks.
+
+Once we solve those issues, we'll publish experimental docs and share that it's ready to try.
+
+---
+
+## Automatic Effect Dependencies {/*automatic-effect-dependencies*/}
+
+When we released hooks, we had three motivations:
+
+- **Sharing code between components**: hooks replaced patterns like render props and higher-order components to allow you to reuse stateful logic without changing your component hierarchy.
+- **Think in terms of function, not lifecycles**: hooks let you split one component into smaller functions based on what pieces are related (such as setting up a subscription or fetching data), rather than forcing a split based on lifecycle methods.
+- **Support ahead-of-time compilation**: hooks were designed to support ahead-of-time compilation with less pitfalls causing unintentional de-optimizations caused by lifecycle methods, and limitations of classes.
+
+Since their release, hooks have been successful at *sharing code between components*. Hooks are now the favored way to share logic between components, and there are less use cases for render props and higher order components. Hooks have also been successful at supporting features like Fast Refresh that were not possible with class components. 
+
+### Effects can be hard {/*effects-can-be-hard*/}
+
+Unfortunately, some hooks are still hard to think in terms of function instead of lifecycles. Effects specifically are still hard to understand and are the most common pain point we hear from developers. Last year, we spent a significant amount of time researching how Effects were used, and how those use cases could be simplified and easier to understand.
+
+We found that often, the confusion is from using an Effect when you don't need to. The [You Might Not Need an Effect](/learn/you-might-not-need-an-effect) guide covers many cases for when Effects are not the right solution. However, even when an Effect is the right fit for a problem, Effects can still be harder to understand than class component lifecycles.
+
+We believe one of the reasons for confusion is that developers to think of Effects from the _component's_ perspective (like a lifecycle), instead of the _Effects_ point of view (what the Effect does).
+
+Let's look at an example [from the docs](/learn/lifecycle-of-reactive-effects#thinking-from-the-effects-perspective):
+
+```js
+useEffect(() => {
+  // Your Effect connected to the room specified with roomId...
+  const connection = createConnection(serverUrl, roomId);
+  connection.connect();
+  return () => {
+    // ...until it disconnected
+    connection.disconnect();
+  };
+}, [roomId]);
+```
+
+Many users would read this code as "on mount, connect to the roomId. whenever `roomId` changes, disconnect to the old room and re-create the connection". However, this is thinking from the component's lifecycle perspective, which means you will need to think of every component lifecycle state to write the Effect correctly. This can be difficult, so it's understandable that Effects seem harder than class lifecycles when using the component perspective.
+
+### Effects without dependencies {/*effects-without-dependencies*/}
+
+Instead, it's better to think from the Effect's perspective. The Effect doesn't know about the component lifecycles. It only describes how to start synchronization and how to stop it. When users think of Effects in this way, their Effects tend to be easier to write, and more resilient to being started and stopped as many times as is needed.
+
+We spent some time researching why Effects are thought of from the component perspective, and we think one of the reasons is the dependency array. Since you have to write it, it's right there and in your face reminding you of what you're "reacting" to and baiting you into the mental model of 'do this when these values change'.
+
+When we released hooks, we knew we could make them easier to use with ahead-of-time compilation. With the React Compiler, you're now able to avoid writing `useCallback` and `useMemo` yourself in most cases. For Effects, the compiler can insert the dependencies for you:
+
+```js
+useEffect(() => {
+  const connection = createConnection(serverUrl, roomId);
+  connection.connect();
+  return () => {
+    connection.disconnect();
+  };
+}); // compiler inserted dependencies. 
+```
+
+With this code, the React Compiler can infer the dependencies for you and insert them automatically so you don't need to see or write them. With features like [the IDE extension](#compiler-ide-extension) and [`useEffectEvent`](/reference/react/experimental_useEffectEvent), we can provide a CodeLens to show you what the Compiler inserted for times you need to debug, or to optimize by removing a dependency. This helps reinforce the correct mental model for writing Effects, which can run at any time to synchronize your component or hook's state with something else.
+
+Our hope is that automatically inserting dependencies is not only easier to write, but that it also makes them easier to understand by forcing you to think in terms of what the Effect does, and not in component lifecycles. 
+
+---
+
+## Compiler IDE Extension {/*compiler-ide-extension*/}
+
+Earlier this week [we shared](/blog/2025/04/21/react-compiler-rc) the React Compiler release candidate, and we're working towards shipping the first SemVer stable version of the compiler in the coming months.
+
+We've also begun exploring ways to use the React Compiler to provide information that can improve understanding and debugging your code. One idea we've started exploring is a new experimental LSP-based React IDE extension powered by React Compiler, similar to the extension used in [Lauren Tan's React Conf talk](https://conf2024.react.dev/talks/5).
+
+Our idea is that we can use the compiler's static analysis to provide more information, suggestions, and optimization opportunities directly in your IDE. For example, we can provide diagnostics for code breaking the Rules of React, hovers to show if components and hooks were optimized by the compiler, or a CodeLens to see [automatically inserted Effect dependencies](#automatic-effect-dependencies).
+
+The IDE extension is still an early exploration, but we'll share our progress in future updates.
+
+---
+
+## Fragment Refs {/*fragment-refs*/}
+
+Many DOM APIs like those for event management, positioning, and focus are difficult to compose when writing with React. This often leads developers to reach for Effects, managing multiple Refs, by using APIs like `findDOMNode` (removed in React 19).
+
+We are exploring adding refs to Fragments that would point to a group of DOM elements, rather than just a single element. Our hope is that this will simplify managing multiple children and make it easier to write composable React code when calling DOM APIs.
+
+Fragment refs are still being researched. We'll share more when we're closer to having the final API finished.
+
+---
+
+## Gesture Animations {/*gesture-animations*/}
+
+We're also researching ways to enhance View Transitions to support gesture animations such as swiping to open a menu, or scroll through a photo carousel. 
+
+Gestures present new challenges for a few reasons:
+
+- **Gestures are continuous**: as you swipe the animation is tied to your finger placement time, rather than triggering and running to completion.
+- **Gestures don't complete**: when you release your finger gesture animations can run to completion, or revert to their original state (like when you only partially open a menu) depending on how far you go.
+- **Gestures invert old and new**: while you're animating, you want the page you are animating from to stay "alive" and interactive. This inverts the browser View Transition model where the "old" state is a snapshot and the "new" state is the live DOM.
+
+We believe we’ve found an approach that works well and may introduce a new API for triggering gesture transitions. For now, we're focused on shipping `<ViewTransition>`, and will revisit gestures afterward.
+
+---
+
+## Concurrent Stores {/*concurrent-stores*/}
+
+When we released React 18 with concurrent rendering, we also released `useSyncExternalStore` so external store libraries that did not use React state or context could [support concurrent rendering](https://github.com/reactwg/react-18/discussions/70) by forcing a synchronous render when the store is updated.
+
+Using `useSyncExternalStore` comes at a cost though, since it forces a bail out from concurrent features like transitions, and forces existing content to show Suspense fallbacks.
+
+Now that React 19 has shipped, we're revisiting this problem space to create a primitive to fully support concurrent external stores with the `use` API:
+
+```js
+const value = use(store);
+```
+
+Our goal is to allow external state to be read during render without tearing, and to work seamlessly with all of the concurrent features React offers. 
+
+This research is still early. We'll share more, and what the new APIs will look like, when we're further along. 
+
+---
+
+_Thanks to [Aurora Scharff](https://bsky.app/profile/aurorascharff.no), [Dan Abramov](https://bsky.app/profile/danabra.mov), [Eli White](https://twitter.com/Eli_White), [Lauren Tan](https://bsky.app/profile/no.lol), [Luna Wei](https://github.com/lunaleaps), [Matt Carroll](https://twitter.com/mattcarrollcode), [Jack Pope](https://jackpope.me), [Jason Bonta](https://threads.net/someextent), [Jordan Brown](https://github.com/jbrown215), [Jordan Eldredge](https://bsky.app/profile/capt.dev), [Mofei Zhang](https://threads.net/z_mofei), [Sebastien Lorber](https://bsky.app/profile/sebastienlorber.com), [Sebastian Markbåge](https://bsky.app/profile/sebmarkbage.calyptus.eu), and [Tim Yung](https://github.com/yungsters) for reviewing this post._
\ No newline at end of file
diff --git a/src/content/blog/index.md b/src/content/blog/index.md
index edde294551..2c19a3a860 100644
--- a/src/content/blog/index.md
+++ b/src/content/blog/index.md
@@ -11,6 +11,12 @@ title: React Blog
 
 <div className="sm:-mx-5 flex flex-col gap-5 mt-12">
 
+<BlogCard title="React Labs: View Transitions, Activity, and more" date="April 23, 2025" url="/blog/2025/04/23/react-labs-view-transitions-activity-and-more">
+
+In React Labs posts, we write about projects in active research and development. In this post, we're sharing two new experimental features that are ready to try today, and sharing other areas we're working on now ...
+
+</BlogCard>
+
 <BlogCard title="React Compiler RC" date="April 21, 2025" url="/blog/2025/04/21/react-compiler-rc">
 
 我们今天将发布 React Compiler 的第一个候选发布版（RC）。
diff --git a/src/content/community/conferences.md b/src/content/community/conferences.md
index 17dd961592..a2bcd196e4 100644
--- a/src/content/community/conferences.md
+++ b/src/content/community/conferences.md
@@ -25,6 +25,11 @@ May 27 - 31, 2025. In-person in Athens, Greece
 
 [Website](https://athens.cityjsconf.org/) - [Twitter](https://x.com/cityjsconf) - [Bluesky](https://bsky.app/profile/cityjsconf.bsky.social)
 
+### React Norway 2025 {/*react-norway-2025*/}
+June 13, 2025. In-person in Oslo, Norway + remote (virtual event)
+
+[Website](https://reactnorway.com/) - [Twitter](https://x.com/ReactNorway)
+
 ### React Summit 2025 {/*react-summit-2025*/}
 June 13 - 17, 2025. In-person in Amsterdam, Netherlands + remote (hybrid event)
 
@@ -50,6 +55,16 @@ October 31 - November 01, 2025. In-person in Goa, India (hybrid event) + Oct 15
 
 [Website](https://www.reactindia.io) - [Twitter](https://twitter.com/react_india) - [Facebook](https://www.facebook.com/ReactJSIndia) - [Youtube](https://www.youtube.com/channel/UCaFbHCBkPvVv1bWs_jwYt3w)
 
+### React Summit US 2025 {/*react-summit-us-2025*/}
+November 18 - 21, 2025. In-person in New York, USA + remote (hybrid event)
+
+[Website](https://reactsummit.us/) - [Twitter](https://x.com/reactsummit)
+
+### React Advanced London 2025 {/*react-advanced-london-2025*/}
+November 28 & December 1, 2025. In-person in London, UK + online (hybrid event)
+
+[Website](https://reactadvanced.com/) - [Twitter](https://x.com/reactadvanced)
+
 
 ## Past Conferences {/*past-conferences*/}
 
diff --git a/src/content/learn/creating-a-react-app.md b/src/content/learn/creating-a-react-app.md
index 759b3b69cf..113cbeb140 100644
--- a/src/content/learn/creating-a-react-app.md
+++ b/src/content/learn/creating-a-react-app.md
@@ -32,7 +32,11 @@ title: 创建一个 React 应用
 npx create-next-app@latest
 </TerminalBlock>
 
+<<<<<<< HEAD
 Next.js 由 [Vercel](https://vercel.com/) 维护。你可以 [将 Next.js 应用部署](https://nextjs.org/docs/app/building-your-application/deploying) 到任何支持 Node.js 或 serverless 的托管平台，或者部署到你自己的服务器。 Next.js 也支持 [静态导出](https://nextjs.org/docs/app/building-your-application/deploying/static-exports) 无需服务器。Vercel 还提供可选的付费云服务。
+=======
+Next.js is maintained by [Vercel](https://vercel.com/). You can [deploy a Next.js app](https://nextjs.org/docs/app/building-your-application/deploying) to any hosting provider that supports Node.js or Docker containers, or to your own server. Next.js also supports [static export](https://nextjs.org/docs/app/building-your-application/deploying/static-exports) which doesn't require a server.
+>>>>>>> f94ab10ed435c948751ef931a90dac172ac4189b
 
 ### React Router (v7) {/*react-router-v7*/}
 
diff --git a/src/content/reference/react/Activity.md b/src/content/reference/react/Activity.md
new file mode 100644
index 0000000000..92ee18d447
--- /dev/null
+++ b/src/content/reference/react/Activity.md
@@ -0,0 +1,1161 @@
+---
+title: <Activity>
+version: experimental
+---
+
+<Experimental>
+
+**This API is experimental and is not available in a stable version of React yet.**
+
+You can try it by upgrading React packages to the most recent experimental version:
+
+- `react@experimental`
+- `react-dom@experimental`
+- `eslint-plugin-react-hooks@experimental`
+
+Experimental versions of React may contain bugs. Don't use them in production.
+
+</Experimental>
+
+<Intro>
+
+`<Activity>` lets you hide and show part of the UI.
+
+
+```js
+<Activity mode={mode}>
+  <Page />
+</Activity>
+```
+
+</Intro>
+
+<InlineToc />
+
+---
+
+## Reference {/*reference*/}
+
+### `<Activity>` {/*activity*/}
+
+Wrap a part of the UI in `<Activity>` to manage its visibility state:
+
+```js
+import {unstableActivity as Activity} from 'react';
+
+<Activity mode={isVisible ? 'visible' : 'hidden'}>
+  <Page />
+</Activity>
+```
+
+When "hidden", the `children` of `<Activity />` are not visible on the page. If a new `<Activity>` mounts as "hidden" then it pre-renders the content at lower priority without blocking the visible content on the page, but it does not mount by creating Effects. When a "visible" Activity switches to "hidden" it conceptually unmounts by destroying all the Effects, but saves its state. This allows fast switching between "visible" and "hidden" states without recreating the state for a "hidden" Activity.
+
+In the future, "hidden" Activities may automatically destroy state based on resources like memory.
+
+#### Props {/*props*/}
+
+* `children`: The actual UI you intend to render.
+* **optional** `mode`: Either "visible" or "hidden". Defaults to "visible". When "hidden", updates to the children are deferred to lower priority. The component will not create Effects until the Activity is switched to "visible". If a "visible" Activity switches to "hidden", the Effects will be destroyed. 
+
+#### Caveats {/*caveats*/}
+
+- While hidden, the `children` of `<Activity>` are hidden on the page. 
+- `<Activity>` will unmount all Effects when switching from "visible" to "hidden" without destroying React or DOM state. This means Effects that are expected to run only once on mount will run again when switching from "hidden" to "visible". Conceptually, "hidden" Activities are unmounted, but they are not destroyed either. We recommend using [`<StrictMode>`](/reference/react/StrictMode) to catch any unexpected side-effects from this behavior.
+- When used with `<ViewTransition>`, hidden activities that reveal in a transition will activate an "enter" animation. Visible Activities hidden in a transition will activate an "exit" animation.
+- Parts of the UI wrapped in `<Activity mode="hidden">` are not included in the SSR response.
+- Parts of the UI wrapped in `<Activity mode="visible">` will hydrate at a lower priority than other content.
+
+---
+
+## Usage {/*usage*/}
+
+### Pre-render part of the UI {/*pre-render-part-of-the-ui*/}
+
+You can pre-render part of the UI using `<Activity mode="hidden">`:
+
+```js
+<Activity mode={tab === "posts" ? "visible" : "hidden"}>
+  <PostsTab />
+</Activity>
+```
+
+When an Activity is rendered with `mode="hidden"`, the `children` are not visible on the page, but are rendered at lower priority than the visible content on the page. 
+
+When the `mode` later switches to "visible", the pre-rendered children will mount and become visible. This can be used to prepare parts of the UI the user is likely to interact with next to reduce loading times.
+
+In the following example from [`useTransition`](/reference/react/useTransition#preventing-unwanted-loading-indicators), the `PostsTab` component fetches some data using `use`. When you click the “Posts” tab, the `PostsTab` component suspends, causing the button loading state to appear:
+
+<Sandpack>
+
+```js
+import { Suspense, useState } from 'react';
+import TabButton from './TabButton.js';
+import AboutTab from './AboutTab.js';
+import PostsTab from './PostsTab.js';
+import ContactTab from './ContactTab.js';
+
+export default function TabContainer() {
+  const [tab, setTab] = useState('about');
+  return (
+    <Suspense fallback={<h1>🌀 Loading...</h1>}>
+      <TabButton
+        isActive={tab === 'about'}
+        action={() => setTab('about')}
+      >
+        About
+      </TabButton>
+      <TabButton
+        isActive={tab === 'posts'}
+        action={() => setTab('posts')}
+      >
+        Posts
+      </TabButton>
+      <TabButton
+        isActive={tab === 'contact'}
+        action={() => setTab('contact')}
+      >
+        Contact
+      </TabButton>
+      <hr />
+      {tab === 'about' && <AboutTab />}
+      {tab === 'posts' && <PostsTab />}
+      {tab === 'contact' && <ContactTab />}
+    </Suspense>
+  );
+}
+```
+
+
+```js src/TabButton.js active
+import { useTransition } from 'react';
+
+export default function TabButton({ action, children, isActive }) {
+  const [isPending, startTransition] = useTransition();
+  if (isActive) {
+    return <b>{children}</b>
+  }
+  if (isPending) {
+    return <b className="pending">{children}</b>;
+  }
+  return (
+    <button onClick={() => {
+      startTransition(() => {
+        action();
+      });
+    }}>
+      {children}
+    </button>
+  );
+}
+```
+
+```js src/AboutTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function AboutTab() {
+  return (
+    <ViewTransition>
+      <p>Welcome to my profile!</p>
+    </ViewTransition>
+  );
+}
+```
+
+```js src/PostsTab.js hidden
+import {use, unstable_ViewTransition as ViewTransition} from 'react';
+import { fetchData } from './data.js';
+
+function PostsTab() {
+  const posts = use(fetchData('/posts'));
+  return (
+    <ViewTransition>
+    <ul className="items">
+      {posts.map(post =>
+        <Post key={post.id} title={post.title} />
+      )}
+    </ul>
+      </ViewTransition>
+  );
+}
+
+function Post({ title }) {
+  return (
+    <li className="item">
+      {title}
+    </li>
+  );
+}
+
+export default PostsTab;
+```
+
+```js src/ContactTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function ContactTab() {
+  return (
+    <ViewTransition>
+      <p>
+        Send me a message!
+      </p>
+      <textarea />
+      <p>
+        You can find me online here:
+      </p>
+      <ul>
+        <li>admin@mysite.com</li>
+        <li>+123456789</li>
+      </ul>
+    </ViewTransition>
+  );
+}
+```
+
+
+```js src/data.js hidden
+// Note: the way you would do data fetching depends on
+// the framework that you use together with Suspense.
+// Normally, the caching logic would be inside a framework.
+
+let cache = new Map();
+
+export function fetchData(url) {
+  if (!cache.has(url)) {
+    cache.set(url, getData(url));
+  }
+  return cache.get(url);
+}
+
+async function getData(url) {
+  if (url.startsWith('/posts')) {
+    return await getPosts();
+  } else {
+    throw Error('Not implemented');
+  }
+}
+
+async function getPosts() {
+  // Add a fake delay to make waiting noticeable.
+  await new Promise(resolve => {
+    setTimeout(resolve, 1000);
+  });
+  let posts = [];
+  for (let i = 0; i < 10; i++) {
+    posts.push({
+      id: i,
+      title: 'Post #' + (i + 1)
+    });
+  }
+  return posts;
+}
+```
+
+```css
+body { height: 275px; }
+button { margin-right: 10px }
+b { display: inline-block; margin-right: 10px; }
+.pending { color: #777; }
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest",
+    "toastify-js": "1.12.0"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+In this example, the user needs to wait for the posts to load when clicking on the "Posts" tab.
+
+We can reduce the delay for the "Posts" tab by pre-rendering the inactive Tabs with a hidden `<Activity>`: 
+
+<Sandpack>
+
+```js
+import { Suspense, useState, unstable_Activity as Activity } from "react";
+import TabButton from "./TabButton.js";
+import AboutTab from "./AboutTab.js";
+import PostsTab from "./PostsTab.js";
+import ContactTab from "./ContactTab.js";
+
+export default function TabContainer() {
+  const [tab, setTab] = useState("about");
+  return (
+    <Suspense fallback={<h1>🌀 Loading...</h1>}>
+      <TabButton isActive={tab === "about"} action={() => setTab("about")}>
+        About
+      </TabButton>
+      <TabButton isActive={tab === "posts"} action={() => setTab("posts")}>
+        Posts
+      </TabButton>
+      <TabButton isActive={tab === "contact"} action={() => setTab("contact")}>
+        Contact
+      </TabButton>
+      <hr />
+      <Activity mode={tab === "about" ? "visible" : "hidden"}>
+        <AboutTab />
+      </Activity>
+      <Activity mode={tab === "posts" ? "visible" : "hidden"}>
+        <PostsTab />
+      </Activity>
+      <Activity mode={tab === "contact" ? "visible" : "hidden"}>
+        <ContactTab />
+      </Activity>
+    </Suspense>
+  );
+}
+```
+
+
+```js src/TabButton.js active
+import { useTransition } from 'react';
+
+export default function TabButton({ action, children, isActive }) {
+  const [isPending, startTransition] = useTransition();
+  if (isActive) {
+    return <b>{children}</b>
+  }
+  if (isPending) {
+    return <b className="pending">{children}</b>;
+  }
+  return (
+    <button onClick={() => {
+      startTransition(() => {
+        action();
+      });
+    }}>
+      {children}
+    </button>
+  );
+}
+```
+
+```js src/AboutTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function AboutTab() {
+  return (
+    <ViewTransition>
+      <p>Welcome to my profile!</p>
+    </ViewTransition>
+  );
+}
+```
+
+```js src/PostsTab.js hidden
+import {use, unstable_ViewTransition as ViewTransition} from 'react';
+import { fetchData } from './data.js';
+
+function PostsTab() {
+  const posts = use(fetchData('/posts'));
+  return (
+    <ViewTransition>
+    <ul className="items">
+      {posts.map(post =>
+        <Post key={post.id} title={post.title} />
+      )}
+    </ul>
+      </ViewTransition>
+  );
+}
+
+function Post({ title }) {
+  return (
+    <li className="item">
+      {title}
+    </li>
+  );
+}
+
+export default PostsTab;
+```
+
+```js src/ContactTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function ContactTab() {
+  return (
+    <ViewTransition>
+      <p>
+        Send me a message!
+      </p>
+      <textarea />
+      <p>
+        You can find me online here:
+      </p>
+      <ul>
+        <li>admin@mysite.com</li>
+        <li>+123456789</li>
+      </ul>
+    </ViewTransition>
+  );
+}
+```
+
+
+```js src/data.js hidden
+// Note: the way you would do data fetching depends on
+// the framework that you use together with Suspense.
+// Normally, the caching logic would be inside a framework.
+
+let cache = new Map();
+
+export function fetchData(url) {
+  if (!cache.has(url)) {
+    cache.set(url, getData(url));
+  }
+  return cache.get(url);
+}
+
+async function getData(url) {
+  if (url.startsWith('/posts')) {
+    return await getPosts();
+  } else {
+    throw Error('Not implemented');
+  }
+}
+
+async function getPosts() {
+  // Add a fake delay to make waiting noticeable.
+  await new Promise(resolve => {
+    setTimeout(resolve, 1000);
+  });
+  let posts = [];
+  for (let i = 0; i < 10; i++) {
+    posts.push({
+      id: i,
+      title: 'Post #' + (i + 1)
+    });
+  }
+  return posts;
+}
+```
+
+```css
+body { height: 275px; }
+button { margin-right: 10px }
+b { display: inline-block; margin-right: 10px; }
+.pending { color: #777; }
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest",
+    "toastify-js": "1.12.0"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+---
+
+### Keeping state for part of the UI {/*keeping-state-for-part-of-the-ui*/}
+
+
+You can keep state for parts of the UI by switching `<Activity>` from "visible" to "hidden":
+
+```js
+<Activity mode={tab === "posts" ? "visible" : "hidden"}>
+  <PostsTab />
+</Activity>
+```
+
+When an Activity switches from `mode="visible"` to "hidden", the `children` will become hidden on the page, and unmount by destroying all Effects, but will keep their React and DOM state.
+
+When the `mode` later switches to "visible", the saved state will be re-used when mounting the children by creating all the Effects. This can be used to keep state in parts of the UI the user is likely to interact with again to maintain DOM or React state.
+
+In the following example from [`useTransition`](/reference/react/useTransition#preventing-unwanted-loading-indicators), the `ContactTab` includes a `<textarea>` with a draft message to send. If you enter some text and change to a different tab, then when you click the “Contact” tab again, the draft message is lost:
+
+
+<Sandpack>
+
+```js
+import { Suspense, useState } from 'react';
+import TabButton from './TabButton.js';
+import AboutTab from './AboutTab.js';
+import PostsTab from './PostsTab.js';
+import ContactTab from './ContactTab.js';
+
+export default function TabContainer() {
+  const [tab, setTab] = useState('contact');
+  return (
+    <Suspense fallback={<h1>🌀 Loading...</h1>}>
+      <TabButton
+        isActive={tab === 'about'}
+        action={() => setTab('about')}
+      >
+        About
+      </TabButton>
+      <TabButton
+        isActive={tab === 'posts'}
+        action={() => setTab('posts')}
+      >
+        Posts
+      </TabButton>
+      <TabButton
+        isActive={tab === 'contact'}
+        action={() => setTab('contact')}
+      >
+        Contact
+      </TabButton>
+      <hr />
+      {tab === 'about' && <AboutTab />}
+      {tab === 'posts' && <PostsTab />}
+      {tab === 'contact' && <ContactTab />}
+    </Suspense>
+  );
+}
+```
+
+
+```js src/TabButton.js active
+import { useTransition } from 'react';
+
+export default function TabButton({ action, children, isActive }) {
+  const [isPending, startTransition] = useTransition();
+  if (isActive) {
+    return <b>{children}</b>
+  }
+  if (isPending) {
+    return <b className="pending">{children}</b>;
+  }
+  return (
+    <button onClick={() => {
+      startTransition(() => {
+        action();
+      });
+    }}>
+      {children}
+    </button>
+  );
+}
+```
+
+```js src/AboutTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function AboutTab() {
+  return (
+    <ViewTransition>
+      <p>Welcome to my profile!</p>
+    </ViewTransition>
+  );
+}
+```
+
+```js src/PostsTab.js hidden
+import {use, unstable_ViewTransition as ViewTransition} from 'react';
+import { fetchData } from './data.js';
+
+function PostsTab() {
+  const posts = use(fetchData('/posts'));
+  return (
+    <ViewTransition>
+    <ul className="items">
+      {posts.map(post =>
+        <Post key={post.id} title={post.title} />
+      )}
+    </ul>
+      </ViewTransition>
+  );
+}
+
+function Post({ title }) {
+  return (
+    <li className="item">
+      {title}
+    </li>
+  );
+}
+
+export default PostsTab;
+```
+
+```js src/ContactTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function ContactTab() {
+  return (
+    <ViewTransition>
+      <p>
+        Send me a message!
+      </p>
+      <textarea />
+      <p>
+        You can find me online here:
+      </p>
+      <ul>
+        <li>admin@mysite.com</li>
+        <li>+123456789</li>
+      </ul>
+    </ViewTransition>
+  );
+}
+```
+
+
+```js src/data.js hidden
+// Note: the way you would do data fetching depends on
+// the framework that you use together with Suspense.
+// Normally, the caching logic would be inside a framework.
+
+let cache = new Map();
+
+export function fetchData(url) {
+  if (!cache.has(url)) {
+    cache.set(url, getData(url));
+  }
+  return cache.get(url);
+}
+
+async function getData(url) {
+  if (url.startsWith('/posts')) {
+    return await getPosts();
+  } else {
+    throw Error('Not implemented');
+  }
+}
+
+async function getPosts() {
+  // Add a fake delay to make waiting noticeable.
+  await new Promise(resolve => {
+    setTimeout(resolve, 1000);
+  });
+  let posts = [];
+  for (let i = 0; i < 10; i++) {
+    posts.push({
+      id: i,
+      title: 'Post #' + (i + 1)
+    });
+  }
+  return posts;
+}
+```
+
+```css
+body { height: 275px; }
+button { margin-right: 10px }
+b { display: inline-block; margin-right: 10px; }
+.pending { color: #777; }
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest",
+    "toastify-js": "1.12.0"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+This results in losing DOM state the user has input. We can keep the state for the Contact tab by hiding the inactive Tabs with `<Activity>`:
+
+
+<Sandpack>
+
+```js
+import { Suspense, useState, unstable_Activity as Activity } from "react";
+import TabButton from "./TabButton.js";
+import AboutTab from "./AboutTab.js";
+import PostsTab from "./PostsTab.js";
+import ContactTab from "./ContactTab.js";
+
+export default function TabContainer() {
+  const [tab, setTab] = useState("about");
+  return (
+    <Suspense fallback={<h1>🌀 Loading...</h1>}>
+      <TabButton isActive={tab === "about"} action={() => setTab("about")}>
+        About
+      </TabButton>
+      <TabButton isActive={tab === "posts"} action={() => setTab("posts")}>
+        Posts
+      </TabButton>
+      <TabButton isActive={tab === "contact"} action={() => setTab("contact")}>
+        Contact
+      </TabButton>
+      <hr />
+      <Activity mode={tab === "about" ? "visible" : "hidden"}>
+        <AboutTab />
+      </Activity>
+      <Activity mode={tab === "posts" ? "visible" : "hidden"}>
+        <PostsTab />
+      </Activity>
+      <Activity mode={tab === "contact" ? "visible" : "hidden"}>
+        <ContactTab />
+      </Activity>
+    </Suspense>
+  );
+}
+```
+
+
+```js src/TabButton.js active
+import { useTransition } from 'react';
+
+export default function TabButton({ action, children, isActive }) {
+  const [isPending, startTransition] = useTransition();
+  if (isActive) {
+    return <b>{children}</b>
+  }
+  if (isPending) {
+    return <b className="pending">{children}</b>;
+  }
+  return (
+    <button onClick={() => {
+      startTransition(() => {
+        action();
+      });
+    }}>
+      {children}
+    </button>
+  );
+}
+```
+
+```js src/AboutTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function AboutTab() {
+  return (
+    <ViewTransition>
+      <p>Welcome to my profile!</p>
+    </ViewTransition>
+  );
+}
+```
+
+```js src/PostsTab.js hidden
+import {use, unstable_ViewTransition as ViewTransition} from 'react';
+import { fetchData } from './data.js';
+
+function PostsTab() {
+  const posts = use(fetchData('/posts'));
+  return (
+    <ViewTransition>
+    <ul className="items">
+      {posts.map(post =>
+        <Post key={post.id} title={post.title} />
+      )}
+    </ul>
+      </ViewTransition>
+  );
+}
+
+function Post({ title }) {
+  return (
+    <li className="item">
+      {title}
+    </li>
+  );
+}
+
+export default PostsTab;
+```
+
+```js src/ContactTab.js hidden
+import {unstable_ViewTransition as ViewTransition} from 'react';
+
+export default function ContactTab() {
+  return (
+    <ViewTransition>
+      <p>
+        Send me a message!
+      </p>
+      <textarea />
+      <p>
+        You can find me online here:
+      </p>
+      <ul>
+        <li>admin@mysite.com</li>
+        <li>+123456789</li>
+      </ul>
+    </ViewTransition>
+  );
+}
+```
+
+
+```js src/data.js hidden
+// Note: the way you would do data fetching depends on
+// the framework that you use together with Suspense.
+// Normally, the caching logic would be inside a framework.
+
+let cache = new Map();
+
+export function fetchData(url) {
+  if (!cache.has(url)) {
+    cache.set(url, getData(url));
+  }
+  return cache.get(url);
+}
+
+async function getData(url) {
+  if (url.startsWith('/posts')) {
+    return await getPosts();
+  } else {
+    throw Error('Not implemented');
+  }
+}
+
+async function getPosts() {
+  // Add a fake delay to make waiting noticeable.
+  await new Promise(resolve => {
+    setTimeout(resolve, 1000);
+  });
+  let posts = [];
+  for (let i = 0; i < 10; i++) {
+    posts.push({
+      id: i,
+      title: 'Post #' + (i + 1)
+    });
+  }
+  return posts;
+}
+```
+
+```css
+body { height: 275px; }
+button { margin-right: 10px }
+b { display: inline-block; margin-right: 10px; }
+.pending { color: #777; }
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest",
+    "toastify-js": "1.12.0"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+---
+
+## Troubleshooting {/*troubleshooting*/}
+
+### Effects don't mount when an Activity is hidden {/*effects-dont-mount-when-an-activity-is-hidden*/}
+
+When an `<Activity>` is "hidden", all Effects are unmounted. Conceptually, the component is unmounted, but React saves the state for later. 
+
+This is a feature of Activity because it means subscriptions won't be subscribed for hidden parts of the UI, reducing the amount of work for hidden content. It also means cleanup, such as pausing a video (which would be expected if you unmounted without Activity) will fire. When an Activity switches to "visible", it will mount by creating the Effects, which will subscribe and play the video.
+
+Consider the following example, where a different video is played for each button:
+
+
+<Sandpack>
+
+```js
+import { useState, useRef, useEffect } from 'react';
+import './checker.js';
+
+function VideoPlayer({ src, isPlaying }) {
+  const ref = useRef(null);
+
+  useEffect(() => {
+    const videoRef = ref.current;
+    videoRef.play();
+    
+    return () => {
+      videoRef.pause();
+    }
+  }, []);
+
+  return <video ref={ref} src={src} muted loop playsInline/>;
+}
+
+export default function App() {
+  const [video, setVideo] = useState(1);
+  return (
+    <>
+      <div>
+        <button onClick={() => setVideo(1)}>Big Buck Bunny</button>
+        <button onClick={() => setVideo(2)}>Elephants Dream</button>
+      </div>
+      {video === 1 &&
+        <VideoPlayer key={1}
+          // 'Big Buck Bunny' licensed under CC 3.0 by the Blender foundation. Hosted by archive.org
+          src="https://archive.org/download/BigBuckBunny_124/Content/big_buck_bunny_720p_surround.mp4" />
+
+      }
+      {video === 2 && 
+        <VideoPlayer key={2}
+          // 'Elephants Dream' by Orange Open Movie Project Studio, licensed under CC-3.0, hosted by archive.org
+          src="https://archive.org/download/ElephantsDream/ed_1024_512kb.mp4"
+        />
+      }
+    </>
+  );
+}
+```
+
+```js src/checker.js hidden
+let interval = setInterval(() => {
+  const videos = Array.from(document.querySelectorAll('video'));
+  const playing = videos.filter(
+    (v) => !v.paused
+  );
+  if (playing.length > 1) {
+    console.error(`Multiple playing videos: ${playing.length}`);
+  }
+    
+}, 50);
+```
+
+
+```css
+body { height: 275px; }
+button { margin-right: 10px }
+b { display: inline-block; margin-right: 10px; }
+video { width: 300px; margin-top: 10px; }
+```
+
+</Sandpack>
+
+
+Whenever you change videos and come back, the video re-loads from the beginning. To maintain the state, you may try to render both videos, and hide the inactive video in `display: none`. However, this will cause both videos to play at the same time:
+
+
+<Sandpack>
+
+```js
+import { useState, useRef, useEffect } from 'react';
+import VideoChecker from './checker.js';
+
+function VideoPlayer({ src, isPlaying }) {
+  const ref = useRef(null);
+
+  useEffect(() => {
+    const videoRef = ref.current;
+    videoRef.play();
+    
+    return () => {
+      videoRef.pause();
+    }
+  }, []);
+
+  return <video ref={ref} src={src} muted loop playsInline/>;
+}
+
+export default function App() {
+  const [video, setVideo] = useState(1);
+  return (
+    <>
+      <div>
+        <button onClick={() => setVideo(1)}>Big Buck Bunny</button>
+        <button onClick={() => setVideo(2)}>Elephants Dream</button>
+      </div>
+      <div style={{display: video === 1 ? 'block' : 'none'}}>
+        <VideoPlayer
+          // 'Big Buck Bunny' licensed under CC 3.0 by the Blender foundation. Hosted by archive.org
+          src="https://archive.org/download/BigBuckBunny_124/Content/big_buck_bunny_720p_surround.mp4" />
+
+      </div>
+      <div style={{display: video === 2 ? 'block' : 'none'}}>
+        <VideoPlayer
+          // 'Elephants Dream' by Orange Open Movie Project Studio, licensed under CC-3.0, hosted by archive.org
+          src="https://archive.org/download/ElephantsDream/ed_1024_512kb.mp4"
+        />
+      </div>
+      <VideoChecker />
+    </>
+  );
+}
+```
+
+```js src/checker.js hidden
+import {useRef, useEffect} from 'react';
+
+export default function VideoChecker() {
+  const hasLogged = useRef(false);
+
+  useEffect(() => {
+    let interval = setInterval(() => {
+      if (hasLogged.current === false) {
+
+        const videos = Array.from(document.querySelectorAll('video'));
+        const playing = videos.filter(
+          (v) => !v.paused
+        );
+        if (hasLogged.current === false && playing.length > 1) {
+          hasLogged.current = true;
+          console.error(`Multiple playing videos: ${playing.length}`);
+        }
+      }
+
+    }, 50);
+    
+    return () => {
+      hasLogged.current = false;
+      clearInterval(interval);
+    }
+  });
+  
+}
+
+```
+
+
+```css
+body { height: 275px; }
+button { margin-right: 10px }
+b { display: inline-block; margin-right: 10px; }
+video { width: 300px; margin-top: 10px; }
+```
+
+</Sandpack>
+
+This is similar to what would happen if Activity mounted Effects when hidden. Similarly, if Activity didn't unmount Effects when hiding, the videos would continue to play in the background.
+
+Activity solves this by not creating Effects when first rendered as "hidden" and destroying all Effects when switching from "visible" to "hidden":
+
+
+<Sandpack>
+
+```js
+import { useState, useRef, useEffect, unstable_Activity as Activity } from 'react';
+import VideoChecker from './checker.js';
+
+function VideoPlayer({ src, isPlaying }) {
+  const ref = useRef(null);
+
+  useEffect(() => {
+    const videoRef = ref.current;
+    videoRef.play();
+    
+    return () => {
+      videoRef.pause();
+    }
+  }, []);
+
+  return <video ref={ref} src={src} muted loop playsInline/>;
+}
+
+export default function App() {
+  const [video, setVideo] = useState(1);
+  return (
+    <>
+      <div>
+        <button onClick={() => setVideo(1)}>Big Buck Bunny</button>
+        <button onClick={() => setVideo(2)}>Elephants Dream</button>
+      </div>
+      <Activity mode={video === 1 ? 'visible' : 'hidden'}>
+        <VideoPlayer
+          // 'Big Buck Bunny' licensed under CC 3.0 by the Blender foundation. Hosted by archive.org
+          src="https://archive.org/download/BigBuckBunny_124/Content/big_buck_bunny_720p_surround.mp4" />
+      </Activity>
+      <Activity mode={video === 2 ? 'visible' : 'hidden'}>
+        <VideoPlayer
+          // 'Elephants Dream' by Orange Open Movie Project Studio, licensed under CC-3.0, hosted by archive.org
+          src="https://archive.org/download/ElephantsDream/ed_1024_512kb.mp4"
+        />
+      </Activity>
+      <VideoChecker />
+    </>
+  );
+}
+```
+
+```js src/checker.js hidden
+import {useRef, useEffect} from 'react';
+
+export default function VideoChecker() {
+  const hasLogged = useRef(false);
+
+  useEffect(() => {
+    let interval = setInterval(() => {
+      if (hasLogged.current === false) {
+
+        const videos = Array.from(document.querySelectorAll('video'));
+        const playing = videos.filter(
+          (v) => !v.paused
+        );
+        if (hasLogged.current === false && playing.length > 1) {
+          hasLogged.current = true;
+          console.error(`Multiple playing videos: ${playing.length}`);
+        }
+      }
+
+    }, 50);
+    
+    return () => {
+      hasLogged.current = false;
+      clearInterval(interval);
+    }
+  });
+  
+}
+
+```
+
+```css
+body { height: 275px; }
+button { margin-right: 10px }
+b { display: inline-block; margin-right: 10px; }
+video { width: 300px; margin-top: 10px; }
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest",
+    "toastify-js": "1.12.0"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test --env=jsdom",
+    "eject": "react-scripts eject"
+  }
+}
+```
+
+</Sandpack>
+
+For this reason, it's best to think of Activity conceptually as "unmounting" and "remounting" the component, but saving the React or DOM state for later. In practice, this works as expected if you have followed the [You Might Not Need an Effect](learn/you-might-not-need-an-effect) guide. To eagerly find problematic Effects, we recommend adding [`<StrictMode>`](/reference/react/StrictMode) which will eagerly perform Activity unmounts and mounts to catch any unexpected side-effects. 
+
+### My hidden Activity is not rendered in SSR {/*my-hidden-activity-is-not-rendered-in-ssr*/}
+
+When you use `<Activity mode="hidden">` during server-side rendering, the content of the Activity will not be included in the SSR response. This is because the content is not visible on the page and is not needed for the initial render. If you need to include the content in the SSR response, you can use a different approach like [`useDeferredValue`](/reference/react/useDeferredValue) to defer rendering of the content.
diff --git a/src/content/reference/react/ViewTransition.md b/src/content/reference/react/ViewTransition.md
new file mode 100644
index 0000000000..a82857f2e9
--- /dev/null
+++ b/src/content/reference/react/ViewTransition.md
@@ -0,0 +1,2213 @@
+---
+title: <ViewTransition>
+version: experimental
+---
+
+<Experimental>
+
+**This API is experimental and is not available in a stable version of React yet.**
+
+You can try it by upgrading React packages to the most recent experimental version:
+
+- `react@experimental`
+- `react-dom@experimental`
+- `eslint-plugin-react-hooks@experimental`
+
+Experimental versions of React may contain bugs. Don't use them in production.
+
+</Experimental>
+
+<Intro>
+
+`<ViewTransition>` lets you animate elements that update inside a Transition.
+
+
+```js
+import {unstableViewTransition as ViewTransition} from 'react';
+
+<ViewTransition>
+  <div>...</div>
+</ViewTransition>
+```
+
+</Intro>
+
+<InlineToc />
+
+---
+
+## Reference {/*reference*/}
+
+### `<ViewTransition>` {/*viewtransition*/}
+
+Wrap elements in `<ViewTransition>` to animate them when they update inside a [Transition](/reference/react/useTransition). React uses the following heuristics to determine if a View Transition activates for an animation:
+
+- `enter`: If a `ViewTransition` itself gets inserted in this Transition, then this will activate.
+- `exit`: If a `ViewTransition` itself gets deleted in this Transition, then this will activate.
+- `update`: If a `ViewTransition` has any DOM mutations inside it that React is doing (such as a prop changing) or if the `ViewTransition` boundary itself changes size or position due to an immediate sibling. If there are nested` ViewTransition` then the mutation applies to them and not the parent.
+- `share`: If a named `ViewTransition` is inside a deleted subtree and another named `ViewTransition` with the same name is part of an inserted subtree in the same Transition, they form a Shared Element Transition, and it animates from the deleted one to the inserted one.
+
+By default, `<ViewTransition>` animates with a smooth cross-fade (the browser default view transition). You can customize the animation by providing a [View Transition Class](#view-transition-class) to the `<ViewTransition>` component. You can  customize animations for each kind of trigger (see [Styling View Transitions](#styling-view-transitions)).
+
+<DeepDive>
+
+#### How does `<ViewTransition>` work? {/*how-does-viewtransition-work*/}
+
+Under the hood, React applies `view-transition-name` to inline styles of the nearest DOM node nested inside the `<ViewTransition>` component. If there are multiple sibling DOM nodes like `<ViewTransition><div /><div /></ViewTransition>` then React adds a suffix to the name to make each unique but conceptually they're part of the same one. React doesn't apply these eagerly but only at the time that boundary should participate in an animation.
+
+React automatically calls `startViewTransition` itself behind the scenes so you should never do that yourself. In fact, if you have something else on the page running a ViewTransition React will interrupt it. So it's recommended that you use React itself to coordinate these. If you had other ways of trigger ViewTransitions in the past, we recommend that you migrate to the built-in way.
+
+If there are other React ViewTransitions already running then React will wait for them to finish before starting the next one. However, importantly if there are multiple updates happening while the first one is running, those will all be batched into one. If you start A->B. Then in the meantime you get an update to go to C and then D. When the first A->B animation finishes the next one will animate from B->D.
+
+The `getSnapshotBeforeUpdate` life-cycle will be called before `startViewTransition` and some `view-transition-name` will update at the same time.
+
+Then React calls `startViewTransition`. Inside the `updateCallback`, React will:
+
+- Apply its mutations to the DOM and invoke useInsertionEffects.
+- Wait for fonts to load.
+- Call componentDidMount, componentDidUpdate, useLayoutEffect and refs.
+- Wait for any pending Navigation to finish.
+- Then React will measure any changes to the layout to see which boundaries will need to animate.
+
+After the ready Promise of the `startViewTransition` is resolved, React will then revert the `view-transition-name`. Then React will invoke the `onEnter`, `onExit`, `onUpdate` and `onShare` callbacks to allow for manual programmatic control over the Animations. This will be after the built-in default ones have already been computed.
+
+If a `flushSync` happens to get in the middle of this sequence, then React will skip the Transition since it relies on being able to complete synchronously.
+
+After the finished Promise of the `startViewTransition` is resolved, React will then invoke `useEffect`. This prevents those from interfering with the performance of the Animation. However, this is not a guarantee because if another `setState` happens while the Animation is running it'll still have to invoke the `useEffect` earlier to preserve the sequential guarantees.
+
+</DeepDive>
+
+#### Props {/*props*/}
+
+By default, `<ViewTransition>` animates with a smooth cross-fade. You can customize the animation, or specify a shared element transition, with these props:
+
+* **optional** `enter`: A string or object. The [View Transition Class](#view-transition-class) to apply when enter is activated.
+* **optional** `exit`: A string or object. The [View Transition Class](#view-transition-class) to apply when exit is activated.
+* **optional** `update`: A string or object. The [View Transition Class](#view-transition-class) to apply when an update is activated.
+* **optional** `share`: A string or object. The [View Transition Class](#view-transition-class) to apply when a shared element is activated.
+* **optional** `default`: A string or object. The [View Transition Class](#view-transition-class) used when no other matching activation prop is found. 
+* **optional** `name`: A string or object. The name of the View Transition used for shared element transitions. If not provided, React will use a unique name for each View Transition to prevent unexpected animations.
+
+#### Callback {/*events*/}
+
+These callbacks allow you to adjust the animation imperatively using the [animate](https://developer.mozilla.org/en-US/docs/Web/API/Element/animate) APIs:
+
+* **optional** `onEnter`: A function. React calls `onEnter` after an "enter" animation.
+* **optional** `onExit`: A function. React calls `onExit` after an "exit" animation.
+* **optional** `onShare`:  A function. React calls `onShare` after a "share" animation.
+* **optional** `onUpdate`:  A function. React calls `onUpdate` after an "update" animation.
+
+Each callback receives as arguments:
+- `element`: The DOM element that was animated.
+- `types`: The [Transition Types](/reference/react/addTransitionType) included in the animation.
+
+### View Transition Class {/*view-transition-class*/}
+
+The View Transition Class is the CSS class name(s) applied by React during the transition when the ViewTransition activates. It can be a string or an object.
+- `string`: the `class` added on the child elements when activated. If `'none'` is provided, no class will be added.
+- `object`: the class added on the child elements will be the key matching View Transition type added with `addTransitionType`. The object can also specify a `default` to use if no matching type is found.
+
+The value `'none'` can be used to prevent a View Transition from activating for a specific trigger.
+
+### Styling View Transitions {/*styling-view-transitions*/}
+
+<Note>
+
+In many early examples of View Transitions around the web, you'll have seen using a [`view-transition-name`](https://developer.mozilla.org/en-US/docs/Web/CSS/view-transition-name) and then style it using `::view-transition-...(my-name)` selectors. We don't recommend that for styling. Instead, we normally recommend using a View Transition Class instead.
+
+</Note>
+
+To customize the animation for a `<ViewTransition>` you can provide a View Transition Class to one of the activation props. The View Transition Class is a CSS class name that React applies to the child elements when the ViewTransition activates.
+
+For example, to customize an "enter" animation, provide a class name to the `enter` prop:
+
+
+```js
+<ViewTransition enter="slide-in">
+```
+
+When the `<ViewTransition>` activates an "enter" animation, React will add the class name `slide-in`. Then you can refer to this class using [view transition pseudo selectors](https://developer.mozilla.org/en-US/docs/Web/API/View_Transition_API#pseudo-elements) to build reusable animations:
+
+```css
+::view-transition-group(.slide-in) {
+  
+}
+::view-transition-old(.slide-in) {
+
+}
+::view-transition-new(.slide-in) {
+
+}
+```
+In the future, CSS libraries may add built-in animations using View Transition Classes to make this easier to use.
+
+#### Caveats {/*caveats*/}
+
+- By default, `setState` updates immediately and does not activate `<ViewTransition>`, only updates wrapped in a [Transition](/reference/react/useTransition). You can also use [`<Suspense>`](/reference/react/Suspense) to opt-in to a Transition to [reveal content](/link-to-suspense-below).
+- `<ViewTransition>` creates an image that can be moved around, scaled and cross-faded. Unlike Layout Animations you may have seen in React Native or Motion, this means that not every individual Element inside of it animates its position. This can lead to better performance and a more continuous feeling, smooth animation compared to animating every individual piece. However, it can also lose continuity in things that should be moving by themselves. So you might have to add more `<ViewTransition>` boundaries manually as a result.
+- Many users may prefer not having animations on the page. React doesn't automatically disable animations for this case. We recommend that using the `@media (prefers-reduced-motion)` media query to disable animations or tone them down based on user preference. In the future, CSS libraries may have this built-in to their presets.
+- Currently, `<ViewTransition>` only works in the DOM. We're working on adding support for React Native and other platforms.
+
+---
+
+
+## Usage {/*usage*/}
+
+### Animating an element on enter/exit {/*animating-an-element-on-enter*/}
+
+Enter/Exit Transitions trigger when a `<ViewTransition>` is added or removed by a component in a transition:
+
+```js
+function Child() {
+  return <ViewTransition>Hi</ViewTransition>
+}
+
+function Parent() {
+  const [show, setShow] = useState();
+  if (show) {
+    return <Child />;
+  }
+  return null;
+}
+```
+
+When `setShow` is called, `show` switches to `true` and the `Child` component is rendered. When `setShow` is called inside `startTransition`, and `Child` renders a `ViewTransition` before any other DOM nodes, an `enter` animation is triggered. 
+
+When `show` switches back to `false`, an `exit` animation is triggered.
+
+<Sandpack>
+
+```js src/Video.js hidden
+function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    />
+  );
+}
+
+export function Video({ video }) {
+  return (
+    <div className="video">
+      <div
+        className="link"
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  useState,
+  startTransition
+} from 'react';
+import {Video} from "./Video";
+import videos from "./data"
+
+function Item() {
+  return (
+    <ViewTransition>
+      <Video video={videos[0]}/>
+    </ViewTransition>
+  );
+}
+
+export default function Component() {
+  const [showItem, setShowItem] = useState(false);
+  return (
+    <>
+      <button
+        onClick={() => {
+          startTransition(() => {
+            setShowItem((prev) => !prev);
+          });
+        }}
+      >{showItem ? '➖' : '➕'}</button>
+
+      {showItem ? <Item /> : null}
+    </>
+  );
+}
+```
+
+```js src/data.js hidden
+export default [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  }
+]
+```
+
+
+```css
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  min-height: 200px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+<Pitfall>
+
+`<ViewTransition>` only activates if it is placed before any DOM node. If `Child` instead looked like this, no animation would trigger:
+
+```js [3, 5]
+function Component() {
+  return (
+    <div>
+      <ViewTransition>Hi</ViewTransition>
+    </div>
+  );
+}
+```
+
+</Pitfall>
+
+---
+### Animating a shared element {/*animating-a-shared-element*/}
+
+Normally, we don't recommend assigning a name to a `<ViewTransition>` and instead let React assign it an automatic name. The reason you might want to assign a name is to animate between completely different components when one tree unmounts and another tree mounts at the same time. To preserve continuity.
+
+```js
+<ViewTransition name={UNIQUE_NAME}>
+  <Child />
+</ViewTransition>
+```
+
+When one tree unmounts and another mounts, if there's a pair where the same name exists in the unmounting tree and the mounting tree, they trigger the "share" animation on both. It animates from the unmounting side to the mounting side.
+
+Unlike an exit/enter animation this can be deeply inside the deleted/mounted tree. If a `<ViewTransition>` would also be eligible for exit/enter, then the "share" animation takes precedence.
+
+If Transition first unmounts one side and then leads to a `<Suspense>` fallback being shown before eventually the new name being mounted, then no shared element transition happens.
+
+<Sandpack>
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  useState,
+  startTransition
+} from "react";
+import {Video, Thumbnail, FullscreenVideo} from "./Video";
+import videos from "./data";
+
+export default function Component() {
+  const [fullscreen, setFullscreen] = useState(false);
+  if (fullscreen) {
+    return <FullscreenVideo
+      video={videos[0]}
+      onExit={() => startTransition(() => setFullscreen(false))}
+    />
+  }
+  return <Video
+    video={videos[0]}
+    onClick={() => startTransition(() => setFullscreen(true))}
+  />
+}
+
+```
+
+```js src/Video.js
+import {unstable_ViewTransition as ViewTransition} from "react";
+
+const THUMBNAIL_NAME = "video-thumbnail"
+
+export function Thumbnail({ video, children }) {
+  return (
+    <ViewTransition name={THUMBNAIL_NAME}>
+      <div
+        aria-hidden="true"
+        tabIndex={-1}
+        className={`thumbnail ${video.image}`}
+      />
+    </ViewTransition>
+  );
+}
+
+export function Video({ video, onClick }) {
+  return (
+    <div className="video">
+      <div className="link" onClick={onClick}>
+        <Thumbnail video={video} />
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+
+export function FullscreenVideo({video, onExit}) {
+  return (
+    <div className="fullscreenLayout">
+      <ViewTransition name={THUMBNAIL_NAME}>
+        <div
+          aria-hidden="true"
+          tabIndex={-1}
+          className={`thumbnail ${video.image} fullscreen`}
+        />
+        <button
+          className="close-button"
+          onClick={onExit}
+        >
+          ✖
+        </button>
+      </ViewTransition>
+    </div>
+  );
+}
+```
+
+
+```js src/data.js hidden
+export default [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  }
+]
+```
+
+
+```css
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  height: 300px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+.thumbnail.fullscreen {
+  height: 100%;
+  width: 100%;
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+.fullscreenLayout {
+  position: relative;
+  height: 100%;
+  width: 100%;
+}
+.close-button {
+  position: absolute;
+  top: 10px;
+  right: 10px;
+  color: black;
+}
+@keyframes progress-animation {
+  from {
+    width: 0;
+  }
+  to {
+    width: 100%;
+  }
+}
+```
+
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+
+<Note>
+
+If either the mounted or unmounted side of a pair is outside the viewport, then no pair is formed. This ensures that it doesn't fly in or out of the viewport when something is scrolled. Instead it's treated as a regular enter/exit by itself.
+
+This does not happen if the same Component instance changes position, which triggers an "update". Those animate regardless if one position is outside the viewport.
+
+There's currently a quirk where if a deeply nested unmounted `<ViewTransition>` is inside the viewport but the mounted side is not within the viewport, then the unmounted side animates as its own "exit" animation even if it's deeply nested instead of as part of the parent animation.
+
+</Note>
+
+<Pitfall>
+
+It's important that there's only one thing with the same name mounted at a time in the entire app. Therefore it's important to use unique namespaces for the name to avoid conflicts. To ensure you can do this you might want to add a constant in a separate module that you import.
+
+```js
+export const MY_NAME = "my-globally-unique-name";
+import {MY_NAME} from './shared-name';
+...
+<ViewTransition name={MY_NAME}>
+```
+
+</Pitfall>
+
+
+---
+
+### Animating reorder of items in a list {/*animating-reorder-of-items-in-a-list*/}
+
+
+```js
+items.map(item => <Component key={item.id} item={item} />)
+```
+
+When reordering a list, without updating the content, the "update" animation triggers on each `<ViewTransition>` in the list if they're outside a DOM node. Similar to enter/exit animations.
+
+This means that this will trigger the animation on this `<ViewTransition>`:
+
+```js
+function Component() {
+  return <ViewTransition><div>...</div></ViewTransition>;
+}
+```
+<Sandpack>
+
+```js src/Video.js hidden
+function Thumbnail({ video }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    />
+  );
+}
+
+export function Video({ video }) {
+  return (
+    <div className="video">
+      <div className="link">
+        <Thumbnail video={video}></Thumbnail>
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  useState,
+  startTransition
+} from "react";
+import {Video} from "./Video";
+import videos from "./data";
+
+export default function Component() {
+  const [orderedVideos, setOrderedVideos] = useState(videos);
+  const reorder = () => {
+    startTransition(() => {
+      setOrderedVideos((prev) => {
+        return [...prev.sort(() => Math.random() - 0.5)];
+      });
+    });
+  };
+  return (
+    <>
+      <button onClick={reorder}>🎲</button>
+      <div className="listContainer">
+        {orderedVideos.map((video, i) => {
+          return (
+            <ViewTransition key={video.title}>
+              <Video video={video} />
+            </ViewTransition>
+          );
+        })}
+      </div>
+    </>
+  );
+}
+  
+
+```
+
+```js src/data.js hidden
+export default [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  }
+]
+```
+
+
+```css
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  min-height: 150px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+```
+
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+However, this wouldn't animate each individual item:
+
+```js
+function Component() {
+  return <div><ViewTransition>...</ViewTransition></div>;
+}
+```
+Instead, any parent `<ViewTransition>` would cross-fade. If there is no parent `<ViewTransition>` then there's no animation in that case.
+
+<Sandpack>
+
+```js src/Video.js hidden
+function Thumbnail({ video }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    />
+  );
+}
+
+export function Video({ video }) {
+  return (
+    <div className="video">
+      <div className="link">
+        <Thumbnail video={video}></Thumbnail>
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  useState,
+  startTransition
+} from "react";
+import {Video} from "./Video";
+import videos from "./data";
+
+export default function Component() {
+  const [orderedVideos, setOrderedVideos] = useState(videos);
+  const reorder = () => {
+    startTransition(() => {
+      setOrderedVideos((prev) => {
+        return [...prev.sort(() => Math.random() - 0.5)];
+      });
+    });
+  };
+  return (
+    <>
+      <button onClick={reorder}>🎲</button>
+      <ViewTransition>
+        <div className="listContainer">
+          {orderedVideos.map((video, i) => {
+            return <Video video={video} key={video.title} />;
+          })}
+        </div>
+      </ViewTransition>
+    </>
+  );
+}
+  
+
+```
+
+```js src/data.js hidden
+export default [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  },
+  {
+    id: '2',
+    title: 'Second video',
+    description: 'Video description',
+    image: 'red',
+  },
+  {
+    id: '3',
+    title: 'Third video',
+    description: 'Video description',
+    image: 'green',
+  },
+  {
+    id: '4',
+    title: 'Fourth video',
+    description: 'Video description',
+    image: 'purple',
+  }
+]
+```
+
+
+```css
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  min-height: 150px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.thumbnail.red {
+  background-image: conic-gradient(at top right, #c76a15, #a6423a, #2b3491);
+}
+.thumbnail.green {
+  background-image: conic-gradient(at top right, #c76a15, #388f7f, #2b3491);
+}
+.thumbnail.purple {
+  background-image: conic-gradient(at top right, #c76a15, #575fb7, #2b3491);
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+```
+
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+This means you might want to avoid wrapper elements in lists where you want to allow the Component to control its own reorder animation:
+
+```
+items.map(item => <div><Component key={item.id} item={item} /></div>)
+```
+
+The above rule also applies if one of the items updates to resize, which then causes the siblings to resize, it'll also animate its sibling `<ViewTransition>` but only if they're immediate siblings.
+
+This means that during an update, which causes a lot of re-layout, it doesn't individually animate every `<ViewTransition>` on the page. That would lead to a lot of noisy animations which distracts from the actual change. Therefore React is more conservative about when an individual animation triggers.
+
+<Pitfall>
+
+It's important to properly use keys to preserve identity when reordering lists. It might seem like you could use "name", shared element transitions, to animate reorders but that would not trigger if one side was outside the viewport. To animate a reorder you often want to show that it went to a position outside the viewport.
+
+</Pitfall>
+
+---
+
+### Animating from Suspense content {/*animating-from-suspense-content*/}
+
+Just like any Transition, React waits for data and new CSS (`<link rel="stylesheet" precedence="...">`) before running the animation. In addition to this, ViewTransitions also wait up to 500ms for new fonts to load before starting the animation to avoid them flickering in later. For the same reason, an image wrapped in ViewTransition will wait for the image to load.
+
+If it's inside a new Suspense boundary instance, then the fallback is shown first. After the Suspense boundary fully loads, it triggers the `<ViewTransition>` to animate the reveal to the content.
+
+Currently, this only happens for client-side Transition. In the future, this will also animate Suspense boundary for streaming SSR when content from the server suspends during the initial load.
+
+There are two ways to animate Suspense boundaries depending on where you place the `<ViewTransition>`:
+
+Update:
+
+```
+<ViewTransition>
+  <Suspense fallback={<A />}>
+    <B />
+  </Suspense>
+</ViewTransition>
+```
+In this scenario when the content goes from A to B, it'll be treated as an "update" and apply that class if appropriate. Both A and B will get the same view-transition-name and therefore they're acting as a cross-fade by default.
+
+<Sandpack>
+
+```js src/Video.js hidden
+function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    />
+  );
+}
+
+export function Video({ video }) {
+  return (
+    <div className="video">
+      <div className="link">
+        <Thumbnail video={video}></Thumbnail>
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+
+export function VideoPlaceholder() {
+  const video = {image: "loading"}
+  return (
+    <div className="video">
+      <div className="link">
+        <Thumbnail video={video}></Thumbnail>
+        <div className="info">
+          <div className="video-title loading" />
+          <div className="video-description loading" />
+        </div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  useState,
+  startTransition,
+  Suspense
+} from 'react';
+import {Video, VideoPlaceholder} from "./Video";
+import {useLazyVideoData} from "./data"
+
+function LazyVideo() {
+  const video = useLazyVideoData();
+  return (
+    <Video video={video}/>
+  );
+}
+
+export default function Component() {
+  const [showItem, setShowItem] = useState(false);
+  return (
+    <>
+      <button
+        onClick={() => {
+          startTransition(() => {
+            setShowItem((prev) => !prev);
+          });
+        }}
+      >{showItem ? '➖' : '➕'}</button>
+      {showItem ? (
+        <ViewTransition>
+          <Suspense fallback={<VideoPlaceholder />}>
+            <LazyVideo />
+          </Suspense>
+        </ViewTransition>
+      ) : null}
+    </>
+  );
+}
+```
+
+```js src/data.js hidden
+import {use} from "react";
+
+let cache = null;
+
+function fetchVideo() {
+  if (!cache) {
+    cache = new Promise((resolve) => {
+      setTimeout(() => {
+        resolve({
+          id: '1',
+          title: 'First video',
+          description: 'Video description',
+          image: 'blue',
+        });
+      }, 1000);
+    });
+  }
+  return cache;
+}
+
+export function useLazyVideoData() {
+  return use(fetchVideo());
+}
+```
+
+
+```css
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  min-height: 200px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.loading {
+  background-image: linear-gradient(90deg, rgba(173, 216, 230, 0.3) 25%, rgba(135, 206, 250, 0.5) 50%, rgba(173, 216, 230, 0.3) 75%);
+  background-size: 200% 100%;
+  animation: shimmer 1.5s infinite;
+}
+@keyframes shimmer {
+  0% {
+    background-position: -200% 0;
+  }
+  100% {
+    background-position: 200% 0;
+  }
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-title.loading {
+  height: 20px;
+  width: 80px;
+  border-radius: 0.5rem;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+  border-radius: 0.5rem;
+}
+.video-description.loading {
+  height: 15px;
+  width: 100px;
+}
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+Enter/Exit:
+
+```
+<Suspense fallback={<ViewTransition><A /></ViewTransition>}>
+  <ViewTransition><B /></ViewTransition>
+</Suspense>
+```
+
+In this scenario, these are two separate ViewTransition instances each with their own `view-transition-name`. This will be treated as an "exit" of the `<A>` and an "enter" of the `<B>`.
+
+You can achieve different effects depending on where you choose to place the `<ViewTransition>` boundary.
+
+---
+### Opting-out of an animation {/*opting-out-of-an-animation*/}
+
+Sometimes you're wrapping a large existing component, like a whole page, and you want to animate some updates, such as changing the theme. However, you don't want it to opt-in all updates inside the whole page to cross-fade when they're updating. Especially if you're incrementally adding more animations.
+
+You can use the class "none" to opt-out of an animation. By wrapping your children in a "none" you can disable animations for updates to them while the parent still triggers.
+
+```js
+<ViewTransition>
+  <div className={theme}>
+    <ViewTransition update="none">
+      {children}
+    </ViewTransition>
+  </div>
+</ViewTransition>
+```
+
+This will only animate if the theme changes and not if only the children update. The children can still opt-in again with their own `<ViewTransition>` but at least it's manual again.
+
+---
+
+### Customizing animations {/*customizing-animations*/}
+
+By default, `<ViewTransition>` includes the default cross-fade from the browser.
+
+To customize animations, you can provide props to the `<ViewTransition>` component to specify which animations to use, based on how the `<ViewTransition>` activates.
+
+For example, we can slow down the default cross fade animation:
+
+```js
+<ViewTransition default="slow-fade">
+  <Video />
+</ViewTransition>
+```
+
+And define slow-fade in CSS using view transition classes:
+
+```css
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+```
+
+<Sandpack>
+
+```js src/Video.js hidden
+function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    />
+  );
+}
+
+export function Video({ video }) {
+  return (
+    <div className="video">
+      <div
+        className="link"
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  useState,
+  startTransition
+} from 'react';
+import {Video} from "./Video";
+import videos from "./data"
+
+function Item() {
+  return (
+    <ViewTransition default="slow-fade">
+      <Video video={videos[0]}/>
+    </ViewTransition>
+  );
+}
+
+export default function Component() {
+  const [showItem, setShowItem] = useState(false);
+  return (
+    <>
+      <button
+        onClick={() => {
+          startTransition(() => {
+            setShowItem((prev) => !prev);
+          });
+        }}
+      >{showItem ? '➖' : '➕'}</button>
+
+      {showItem ? <Item /> : null}
+    </>
+  );
+}
+```
+
+```js src/data.js hidden
+export default [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  }
+]
+```
+
+
+```css
+::view-transition-old(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+::view-transition-new(.slow-fade) {
+    animation-duration: 500ms;
+}
+
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  min-height: 200px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+In addition to setting the `default`, you can also provide configurations for `enter`, `exit`, `update`, and `share` animations.
+
+<Sandpack>
+
+```js src/Video.js hidden
+function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    />
+  );
+}
+
+export function Video({ video }) {
+  return (
+    <div className="video">
+      <div
+        className="link"
+      >
+        <Thumbnail video={video}></Thumbnail>
+
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  useState,
+  startTransition
+} from 'react';
+import {Video} from "./Video";
+import videos from "./data"
+
+function Item() {
+  return (
+    <ViewTransition enter="slide-in" exit="slide-out">
+      <Video video={videos[0]}/>
+    </ViewTransition>
+  );
+}
+
+export default function Component() {
+  const [showItem, setShowItem] = useState(false);
+  return (
+    <>
+      <button
+        onClick={() => {
+          startTransition(() => {
+            setShowItem((prev) => !prev);
+          });
+        }}
+      >{showItem ? '➖' : '➕'}</button>
+
+      {showItem ? <Item /> : null}
+    </>
+  );
+}
+```
+
+```js src/data.js hidden
+export default [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  }
+]
+```
+
+
+```css
+::view-transition-old(.slide-in) {
+  animation-name: slideOutRight;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-new(.slide-in) {
+  animation-name: slideInRight;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-old(.slide-out) {
+  animation-name: slideOutLeft;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-new(.slide-out) {
+  animation-name: slideInLeft;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+@keyframes slideOutLeft {
+  from {
+    transform: translateX(0);
+    opacity: 1;
+  }
+  to {
+    transform: translateX(-100%);
+    opacity: 0;
+  }
+}
+
+@keyframes slideInLeft {
+  from {
+    transform: translateX(-100%);
+    opacity: 0;
+  }
+  to {
+    transform: translateX(0);
+    opacity: 1;
+  }
+}
+
+@keyframes slideOutRight {
+  from {
+    transform: translateX(0);
+    opacity: 1;
+  }
+  to {
+    transform: translateX(100%);
+    opacity: 0;
+  }
+}
+
+@keyframes slideInRight {
+  from {
+    transform: translateX(100%);
+    opacity: 0;
+  }
+  to {
+    transform: translateX(0);
+    opacity: 1;
+  }
+}
+
+@keyframes slideInRight {
+  from {
+    transform: translateX(100%);
+    opacity: 0;
+  }
+  to {
+    transform: translateX(0);
+    opacity: 1;
+  }
+}
+
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  min-height: 200px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+### Customizing animations with types {/*customizing-animations-with-types*/}
+You can use the [`addTransitionType`](/reference/react/addTransitionType) API to add a class name to the child elements when a specific transition type is activated for a specific activation trigger. This allows you to customize the animation for each type of transition.
+
+For example, to customize the animation for all forward and backward navigations:
+
+```js
+<ViewTransition default={{
+  'navigation-back': 'slide-right',
+  'navigation-forward': 'slide-left',
+ }}>
+  <div>...</div>
+</ViewTransition>
+ 
+// in your router:
+startTransition(() => {
+  addTransitionType('navigation-' + navigationType);
+});
+```
+
+When the ViewTransition activates a "navigation-back" animation, React will add the class name "slide-right". When the ViewTransition activates a "navigation-forward" animation, React will add the class name "slide-left".
+
+In the future, routers and other libraries may add support for standard view-transition types and styles.
+
+<Sandpack>
+
+```js src/Video.js hidden
+function Thumbnail({ video, children }) {
+  return (
+    <div
+      aria-hidden="true"
+      tabIndex={-1}
+      className={`thumbnail ${video.image}`}
+    />
+  );
+}
+
+export function Video({ video }) {
+  return (
+    <div className="video">
+      <div
+        className="link"
+      >
+        <Thumbnail video={video}></Thumbnail>
+        <div className="info">
+          <div className="video-title">{video.title}</div>
+          <div className="video-description">{video.description}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+```
+
+```js
+import {
+  unstable_ViewTransition as ViewTransition,
+  unstable_addTransitionType as addTransitionType,
+  useState,
+  startTransition,
+} from "react";
+import {Video} from "./Video";
+import videos from "./data"
+
+function Item() {
+  return (
+    <ViewTransition enter={
+        {
+          "add-video-back": "slide-in-back",
+          "add-video-forward": "slide-in-forward"
+        }
+      }
+      exit={
+        {
+          "remove-video-back": "slide-in-forward",
+          "remove-video-forward": "slide-in-back"
+        }
+      }>
+      <Video video={videos[0]}/>
+    </ViewTransition>
+  );
+}
+
+export default function Component() {
+  const [showItem, setShowItem] = useState(false);
+  return (
+    <>
+      <div className="button-container">
+        <button
+          onClick={() => {
+            startTransition(() => {
+              if (showItem) {
+                addTransitionType("remove-video-back")
+              } else {
+                addTransitionType("add-video-back")
+              }
+              setShowItem((prev) => !prev);
+            });
+          }}
+        >⬅️</button>
+        <button
+          onClick={() => {
+            startTransition(() => {
+              if (showItem) {
+                addTransitionType("remove-video-forward")
+              } else {
+                addTransitionType("add-video-forward")
+              }
+              setShowItem((prev) => !prev);
+            });
+          }}
+        >➡️</button>
+      </div>
+      {showItem ? <Item /> : null}
+    </>
+  );
+}
+```
+
+```js src/data.js hidden
+export default [
+  {
+    id: '1',
+    title: 'First video',
+    description: 'Video description',
+    image: 'blue',
+  }
+]
+```
+
+
+```css
+::view-transition-old(.slide-in-back) {
+  animation-name: slideOutRight;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-new(.slide-in-back) {
+  animation-name: slideInRight;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-old(.slide-out-back) {
+  animation-name: slideOutLeft;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-new(.slide-out-back) {
+  animation-name: slideInLeft;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-old(.slide-in-forward) {
+  animation-name: slideOutLeft;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-new(.slide-in-forward) {
+  animation-name: slideInLeft;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-old(.slide-out-forward) {
+  animation-name: slideOutRight;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+::view-transition-new(.slide-out-forward) {
+  animation-name: slideInRight;
+  animation-duration: 500ms;
+  animation-timing-function: ease-in-out;
+}
+
+@keyframes slideOutLeft {
+  from {
+    transform: translateX(0);
+    opacity: 1;
+  }
+  to {
+    transform: translateX(-100%);
+    opacity: 0;
+  }
+}
+
+@keyframes slideInLeft {
+  from {
+    transform: translateX(-100%);
+    opacity: 0;
+  }
+  to {
+    transform: translateX(0);
+    opacity: 1;
+  }
+}
+
+@keyframes slideOutRight {
+  from {
+    transform: translateX(0);
+    opacity: 1;
+  }
+  to {
+    transform: translateX(100%);
+    opacity: 0;
+  }
+}
+
+@keyframes slideInRight {
+  from {
+    transform: translateX(100%);
+    opacity: 0;
+  }
+  to {
+    transform: translateX(0);
+    opacity: 1;
+  }
+}
+
+@keyframes slideInRight {
+  from {
+    transform: translateX(100%);
+    opacity: 0;
+  }
+  to {
+    transform: translateX(0);
+    opacity: 1;
+  }
+}
+
+#root {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  min-height: 200px;
+}
+button {
+  border: none;
+  border-radius: 50%;
+  width: 50px;
+  height: 50px;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  background-color: #f0f8ff;
+  color: white;
+  font-size: 20px;
+  cursor: pointer;
+  transition: background-color 0.3s, border 0.3s;
+}
+button:hover {
+  border: 2px solid #ccc;
+  background-color: #e0e8ff;
+}
+.button-container {
+  display: flex;
+}
+.thumbnail {
+  position: relative;
+  aspect-ratio: 16 / 9;
+  display: flex;
+  overflow: hidden;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+  border-radius: 0.5rem;
+  outline-offset: 2px;
+  width: 8rem;
+  vertical-align: middle;
+  background-color: #ffffff;
+  background-size: cover;
+  user-select: none;
+}
+.thumbnail.blue {
+  background-image: conic-gradient(at top right, #c76a15, #087ea4, #2b3491);
+}
+.video {
+  display: flex;
+  flex-direction: row;
+  gap: 0.75rem;
+  align-items: center;
+  margin-top: 1em;
+}
+.video .link {
+  display: flex;
+  flex-direction: row;
+  flex: 1 1 0;
+  gap: 0.125rem;
+  outline-offset: 4px;
+  cursor: pointer;
+}
+.video .info {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  margin-left: 8px;
+  gap: 0.125rem;
+}
+.video .info:hover {
+  text-decoration: underline;
+}
+.video-title {
+  font-size: 15px;
+  line-height: 1.25;
+  font-weight: 700;
+  color: #23272f;
+}
+.video-description {
+  color: #5e687e;
+  font-size: 13px;
+}
+```
+
+```json package.json hidden
+{
+  "dependencies": {
+    "react": "experimental",
+    "react-dom": "experimental",
+    "react-scripts": "latest"
+  }
+}
+```
+
+</Sandpack>
+
+### Building View Transition enabled routers {/*building-view-transition-enabled-routers*/}
+
+React waits for any pending Navigation to finish to ensure that scroll restoration happens within the animation. If the Navigation is blocked on React, your router must unblock in `useLayoutEffect` since `useEffect` would lead to a deadlock.
+
+If a `startTransition` is started from the legacy popstate event, such as during a "back"-navigation then it must finish synchronously to ensure scroll and form restoration works correctly. This is in conflict with running a View Transition animation. Therefore, React will skip animations from popstate. Therefore animations won't run for the back button. You can fix this by upgrading your router to use the Navigation API.
+
+---
+
+## Troubleshooting {/*troubleshooting*/}
+
+### My `<ViewTransition>` is not activating {/*my-viewtransition-is-not-activating*/}
+
+`<ViewTransition>` only activates if it is placed is before any DOM node:
+
+```js [3, 5]
+function Component() {
+  return (
+    <div>
+      <ViewTransition>Hi</ViewTransition>
+    </div>
+  );
+}
+```
+
+To fix, ensure that the `<ViewTransition>` comes before any other DOM nodes:
+
+```js [3, 5] 
+function Component() {
+  return (
+    <ViewTransition>
+      <div>Hi</div>
+    </ViewTransition>
+  );
+}
+```
+
+### I'm getting an error "There are two `<ViewTransition name=%s>` components with the same name mounted at the same time." {/*two-viewtransition-with-same-name*/}
+
+This error occurs when two `<ViewTransition>` components with the same `name` are mounted at the same time:
+
+
+```js [3]
+function Item() {
+  // 🚩 All items will get the same "name".
+  return <ViewTransition name="item">...</ViewTransition>;
+}
+
+function ItemList({items}) {
+  return (
+    <>
+      {item.map(item => <Item key={item.id} />)}
+    </>
+  );
+}
+```
+
+This will cause the View Transition to error. In development, React detects this issue to surface it and logs two errors:
+
+<ConsoleBlockMulti>
+<ConsoleLogLine level="error">
+
+There are two `<ViewTransition name=%s>` components with the same name mounted at the same time. This is not supported and will cause View Transitions to error. Try to use a more unique name e.g. by using a namespace prefix and adding the id of an item to the name.
+{'    '}at Item
+{'    '}at ItemList
+
+</ConsoleLogLine>
+
+<ConsoleLogLine level="error">
+
+The existing `<ViewTransition name=%s>` duplicate has this stack trace.
+{'    '}at Item
+{'    '}at ItemList
+
+</ConsoleLogLine>
+</ConsoleBlockMulti>
+
+To fix, ensure that there's only one `<ViewTransition>` with the same name mounted at a time in the entire app by ensuring the `name` is unique, or adding an `id` to the name:
+
+```js [3]
+function Item({id}) {
+  // ✅ All items will get the same "name".
+  return <ViewTransition name={`item-${id}`}>...</ViewTransition>;
+}
+
+function ItemList({items}) {
+  return (
+    <>
+      {item.map(item => <Item key={item.id} item={item} />)}
+    </>
+  );
+}
+```
diff --git a/src/content/reference/react/addTransitionType.md b/src/content/reference/react/addTransitionType.md
new file mode 100644
index 0000000000..f292ea7557
--- /dev/null
+++ b/src/content/reference/react/addTransitionType.md
@@ -0,0 +1,182 @@
+---
+title: unstable_addTransitionType
+version: experimental
+---
+
+<Experimental>
+
+**This API is experimental and is not available in a stable version of React yet.**
+
+You can try it by upgrading React packages to the most recent experimental version:
+
+- `react@experimental`
+- `react-dom@experimental`
+- `eslint-plugin-react-hooks@experimental`
+
+Experimental versions of React may contain bugs. Don't use them in production.
+
+</Experimental>
+
+<Intro>
+
+`unstable_addTransitionType` lets you specify the cause of a transition.
+
+
+```js
+startTransition(() => {
+  unstable_addTransitionType('my-transition-type');
+  setState(newState);
+});
+```
+
+</Intro>
+
+<InlineToc />
+
+---
+
+## Reference {/*reference*/}
+
+### `addTransitionType` {/*addtransitiontype*/}
+
+#### Parameters {/*parameters*/}
+
+- `type`: The type of transition to add. This can be any string.
+
+#### Returns {/*returns*/}
+
+`startTransition` does not return anything.
+
+#### Caveats {/*caveats*/}
+
+- If multiple transitions are combined, all Transition Types are collected. You can also add more than one type to a Transition.
+- Transition Types are reset after each commit. This means a `<Suspense>` fallback will associate the types after a `startTransition`, but revealing the content does not.
+
+---
+
+## Usage {/*usage*/}
+
+### Adding the cause of a transition {/*adding-the-cause-of-a-transition*/}
+
+Call `addTransitionType` inside of `startTransition` to indicate the cause of a transition:
+
+``` [[1, 6, "unstable_addTransitionType"], [2, 5, "startTransition", [3, 6, "'submit-click'"]]
+import { startTransition, unstable_addTransitionType } from 'react';
+
+function Submit({action) {
+  function handleClick() {
+    startTransition(() => {
+      unstable_addTransitionType('submit-click');
+      action();
+    });
+  }
+
+  return <button onClick={handleClick}>Click me</button>;
+}
+
+```
+
+When you call <CodeStep step={1}>addTransitionType</CodeStep> inside the scope of <CodeStep step={2}>startTransition</CodeStep>, React will associate <CodeStep step={3}>submit-click</CodeStep> as one of the causes for the Transition.
+
+Currently, Transition Types can be used to customize different animations based on what caused the Transition. You have three different ways to choose from for how to use them:
+
+- [Customize animations using browser view transition types](#customize-animations-using-browser-view-transition-types)
+- [Customize animations using `View Transition` Class](#customize-animations-using-view-transition-class)
+- [Customize animations using `ViewTransition` events](#customize-animations-using-viewtransition-events) 
+
+In the future, we plan to support more use cases for using the cause of a transition.
+
+---
+### Customize animations using browser view transition types {/*customize-animations-using-browser-view-transition-types*/}
+
+When a [`ViewTransition`](/reference/react/ViewTransition) activates from a transition, React adds all the Transition Types as browser [view transition types](https://www.w3.org/TR/css-view-transitions-2/#active-view-transition-pseudo-examples) to the element.
+
+This allows you to customize different animations based on CSS scopes:
+
+```js [11]
+function Component() {
+  return (
+    <ViewTransition>
+      <div>Hello</div>
+    </ViewTransition>
+  );
+}
+
+startTransition(() => {
+  unstable_addTransitionType('my-transition-type');
+  setShow(true);
+});
+```
+
+```css
+:root:active-view-transition-type(my-transition-type) {
+  &::view-transition-...(...) {
+    ...
+  }
+}
+```
+
+---
+
+### Customize animations using `View Transition` Class {/*customize-animations-using-view-transition-class*/}
+
+You can customize animations for an activated `ViewTransition` based on type by passing an object to the View Transition Class:
+
+```js
+function Component() {
+  return (
+    <ViewTransition enter={{
+      'my-transition-type': 'my-transition-class',
+    }}>
+      <div>Hello</div>
+    </ViewTransition>
+  );
+}
+
+// ...
+startTransition(() => {
+  unstable_addTransitionType('my-transition-type');
+  setState(newState);
+});
+```
+
+If multiple types match, then they're joined together. If no types match then the special "default" entry is used instead. If any type has the value "none" then that wins and the ViewTransition is disabled (not assigned a name).
+
+These can be combined with enter/exit/update/layout/share props to match based on kind of trigger and Transition Type.
+
+```js
+<ViewTransition enter={{
+  'navigation-back': 'enter-right',
+  'navigation-forward': 'enter-left',
+}}
+exit={{
+  'navigation-back': 'exit-right',
+  'navigation-forward': 'exit-left',
+}}>
+```
+
+---
+
+### Customize animations using `ViewTransition` events {/*customize-animations-using-viewtransition-events*/}
+
+You can imperatively customize animations for an activated `ViewTransition` based on type using View Transition events:
+
+```
+<ViewTransition onUpdate={(inst, types) => {
+  if (types.includes('navigation-back')) {
+    ...
+  } else if (types.includes('navigation-forward')) {
+    ...
+  } else {
+    ...
+  }
+}}>
+```
+
+This allows you to pick different imperative Animations based on the cause.
+
+---
+
+## Troubleshooting {/*troubleshooting*/}
+
+### TODO {/*todo2*/}
diff --git a/src/content/reference/react/experimental_taintObjectReference.md b/src/content/reference/react/experimental_taintObjectReference.md
index 35bccc3846..6e19f2c182 100644
--- a/src/content/reference/react/experimental_taintObjectReference.md
+++ b/src/content/reference/react/experimental_taintObjectReference.md
@@ -1,8 +1,9 @@
 ---
 title: experimental_taintObjectReference
+version: experimental
 ---
 
-<Wip>
+<Experimental>
 
 **此实验性 API 尚未在 React 的稳定版本中提供**。
 
@@ -16,7 +17,7 @@ React 的实验版本可能有一些问题，请勿在生产环境中使用。
 
 此 API 仅在 React 服务器组件内可用。
 
-</Wip>
+</Experimental>
 
 
 <Intro>
diff --git a/src/content/reference/react/experimental_taintUniqueValue.md b/src/content/reference/react/experimental_taintUniqueValue.md
index 7cc0516556..aa403f03d5 100644
--- a/src/content/reference/react/experimental_taintUniqueValue.md
+++ b/src/content/reference/react/experimental_taintUniqueValue.md
@@ -1,8 +1,9 @@
 ---
 title: experimental_taintUniqueValue
+version: experimental
 ---
 
-<Wip>
+<Experimental>
 
 **此实验性 API 尚未在 React 的稳定版本中提供**。
 
@@ -16,7 +17,7 @@ React 的实验版本可能有一些问题，请勿在生产环境中使用。
 
 此 API 仅在 [React 服务器组件](/reference/rsc/use-client) 内可用。
 
-</Wip>
+</Experimental>
 
 
 <Intro>
diff --git a/src/content/reference/react/experimental_useEffectEvent.md b/src/content/reference/react/experimental_useEffectEvent.md
index f773455be1..fb0de84a01 100644
--- a/src/content/reference/react/experimental_useEffectEvent.md
+++ b/src/content/reference/react/experimental_useEffectEvent.md
@@ -1,8 +1,9 @@
 ---
 title: experimental_useEffectEvent
+version: experimental
 ---
 
-<Wip>
+<Experimental>
 
 **这是实验性 API，并且在 React 的稳定版中还不可用**。
 
@@ -14,7 +15,7 @@ title: experimental_useEffectEvent
 
 实验性 API 可能存在 bug，所以不要在生产环境使用。
 
-</Wip>
+</Experimental>
 
 
 <Intro>
diff --git a/src/sidebarBlog.json b/src/sidebarBlog.json
index 61e18c0a93..fb0de3a35f 100644
--- a/src/sidebarBlog.json
+++ b/src/sidebarBlog.json
@@ -11,6 +11,13 @@
       "path": "/blog",
       "skipBreadcrumb": true,
       "routes": [
+        {
+          "title": "React Labs: View Transitions, Activity, and more",
+          "titleForHomepage": "View Transitions and Activity",
+          "icon": "blog",
+          "date": "April 23, 2025",
+          "path": "/blog/2025/04/23/react-labs-view-transitions-activity-and-more"
+        },
         {
           "title": "React Compiler RC",
           "titleForHomepage": "React Compiler RC",
diff --git a/src/sidebarReference.json b/src/sidebarReference.json
index e7f3f699b5..f1e439dd89 100644
--- a/src/sidebarReference.json
+++ b/src/sidebarReference.json
@@ -103,6 +103,16 @@
         {
           "title": "<Suspense>",
           "path": "/reference/react/Suspense"
+        },
+        {
+          "title": "<Activity>",
+          "path": "/reference/react/Activity",
+          "version": "experimental"
+        },
+        {
+          "title": "<ViewTransition>",
+          "path": "/reference/react/ViewTransition",
+          "version": "experimental"
         }
       ]
     },
@@ -144,12 +154,17 @@
         {
           "title": "experimental_taintObjectReference",
           "path": "/reference/react/experimental_taintObjectReference",
-          "version": "canary"
+          "version": "experimental"
         },
         {
           "title": "experimental_taintUniqueValue",
           "path": "/reference/react/experimental_taintUniqueValue",
-          "version": "canary"
+          "version": "experimental"
+        },
+        {
+          "title": "unstable_addTransitionType",
+          "path": "/reference/react/addTransitionType",
+          "version": "experimental"
         }
       ]
     },