This is to investigate optimizing how we load OOjs UI in MediaWiki. I have some thoughts I have written down on another machine, that all seemed fairly easy to implement. They don't seem like large gains, but may be worth it.
[ ] CSS minifier:
[ ] Remove whitespace around CSS selectors: `a + b`, `a > b`, etc.
[ ] Remove whitespace inside parentheses: `( foo )`
[ ] Remove `"` from url() values and attribute selectors: `url( "img.src" )`, `[type="radio"]`
[ ] Remove leading `0` from fractional CSS values: `0.8em`
[ ] Ensure hex colors are output in shorthand notation: `#fff` (Less compiler sets them back to 6-digit notation in contrast to f.e. Sass)
[ ] Icons and stuff:
[ ] Remove domain from URLs like `//xx.wikipedia.org/w/load.php?...`
[ ] Remove whitespace and ids from embedded SVG files
[ ] Reconsider Flow's use of .mw-ui-hovericon (dropdown menu items that gain progressive/constructive/destructive styling on hover) – T110051
[x] Do something magical to avoid double-loading 'oojs-ui.styles' and friends due to T87871.