Fix experimental notice in FF ESR

[brandonpayton]

What is this PR doing?

Fixes #1106 where the experimental notice takes over most of the content area.

What problem is it solving?

The experiemental-and-fun notice is styled with nested CSS which is not supported by Firefox ESR v115.x. Firefox v117.x introduced CSS nesting support.

How is the problem addressed?

This PR removes use of nested CSS for now.

Testing Instructions

• Install and launch Firefox ESR v115.x
• Run npm run dev
• Navigate to http://localhost:5400/website-server/ and observe the large notice
• If the notice is missing, clear cookies for the current site and reload the page.
• Apply this patch
• Clear cookies for the current site, reload the page, and observe the notice is displayed reasonably at the bottom of the screen.

NOTE: Playground is failing to load in FF ESR from localhost, but it is likely unrelated. This is just a CSS change, and the problem occurs on both trunk and this branch.

[adamziel]

This is lovely, thank you @brandonpayton! This will auto-deploy at 9am utc