Replacing 'mediawiki.ui/variables.less' `@import`
with new skin-aware 'mediawiki.skin.variables.less' standard.
Also
- replacing several static values with skin variables featuring new
Codex design tokens for following properties:
- background-color
- color
- border-width, border-style, border-color and border shorthand
Bump required MediaWiki core version to >= v1.41.0.
Bug: T319381
Bug: T332541
Depends-On: I04f9e48a1cf9dee915cf51e1e12b17ff0a595a06
Change-Id: I32c2996dedc9b3a54e1f916623dbe1c4da910083
For IntersectionObserver to work the element we listen on needs to
have a non-zero height.
Bug: T223844
Change-Id: I308f646670b112e42b0aaa11c438dbc5cdc5edd8