Add underline to high contrast text when prefers-contrast is active (#1141)

* Add underline to high contrast text when prefers-contrast is active

* Add guide class to ensure only body text is underlined

* Update _variables.scss

Changed to a 1 px thickness and offset for a tighter, cleaner, look and feel.

Author: jason-me

_sass/minima/_variables.scss

@@ -58,6 +58,12 @@ $primary-color: $bitcoin-yellow;
     --primary-color-s: 72%;
     --primary-color-l: 35%;
     --primary-color-l-darker: 25%;
+    
+    .guide a {
+      text-decoration: underline;
+      text-decoration-thickness: 1px;
+      text-underline-offset: 1px;
+    }
   }
 }