Fix playground handling of visible scrollbars (#1514)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1514

On machines with scrollbars, we shouldn't show them unconditionally, and the toolbar should be in the area within them.

This also fixes a couple bugs:
1. Preview not rendering based on correct code when light/dark mode changes
2. Crash on start on mobile safari
3. Incorrect rendering of preview on mobile safari

This also fixes a bug where the playground re-rendering (e.g. on theme change) makes the preview snap back to the initial code passes.

https://yoga-website-next-git-fork-nickgerleman-exp-194d90-fbopensource.vercel.app/

Reviewed By: shwanton

Differential Revision: D52145666

fbshipit-source-id: 50184305987aab4cbcd066f37582997dfdc78c02

website-next/src/pages/index.module.css

@@ -22,11 +22,11 @@
 @media (max-width: 996px) {
   .heroLogo {
     display: none;
-   }
+  }
 
-   .playgroundSection :global(.prism-code) {
+  .playgroundSection :global(.playground-editor) {
     display: none;
-   }
+  }
 }
 
 .bg {