Update book.js

Update book.js

Update book.js

Revert "Update book.js"

This reverts commit 0ed9477.

Update book.js

Author: expikr

src/theme/book.js

@@ -360,13 +360,13 @@ function playground_text(playground, hidden = true) {
         }
 
         var previousTheme = get_theme();
-
+        var themeId = theme.replace(/\W+/g, '_').toLowerCase();
         if (store) {
-            try { localStorage.setItem('mdbook-theme', theme); } catch (e) { }
+            try { localStorage.setItem('mdbook-theme', themeId); } catch (e) { }
         }
 
         html.classList.remove(previousTheme);
-        html.classList.add(theme);
+        html.classList.add(themeId);
         updateThemeSelected();
     }