fix(wiki.nixos.org): missing variables & fixes

[nuexq]

🔧 What does this fix? 🔧

old	now

• Added the following variables:
  • background-color-base-fixed
  • background-color-neutral-subtle
  • color-progressive
  • border-color-progressive
  • border-color-progressive--focus
  • border-color-muted
• Added the following variables for .box and .box-content:
  • box-color-impl
  • box-background-impl
  • box-border-color-impl
  • color-base
• Fixed copy button hover colors on code blocks.
• Remove background and border from hamburger menu to match the original style.

🗒 Checklist 🗒

• I have read and followed Catppuccin's contributing guidelines.

[uncenter]

Putting this on hold as we plan to transition to using a MediaWiki library module to use for the Wikipedia and wiki.nixos.org userstyles, and some if not all of these changes would be made there.