The CSS Working Group publishes a page with all of the things that they'd like to fix in CSS but can't because the "mistakes" are already in the wild and changing them would break the web—an unforgivable sin. Here are a few of my favorites:
- z-index should be called z-order or depth and should Just Work on all elements (like it does on flex items).
- The alignment properties in Flexbox should have been writing-mode relative, not flex-flow relative, and thus could have reasonably understandable names like align-inline-* and align-block-*.
- It shouldn't be !important — that reads to engineers as “not important”. We should have picked another way to write this.
- Not quite a mistake, because it was a reasonable default for the 90s, but it would be more helpful since then if `background-repeat` defaulted to `no-repeat`.
- Box-sizing should be border-box by default.
And finally, the funniest one:
- Table layout should be sane.
https://wiki.csswg.org/ideas/mistakes
https://blakewatson.com/links/2026-02-10-incomplete-list-of-mistakes-in-the-design-of-css/