It's fun to see which technical decisions the CSS working group officially consider "mistakes" 😂 I agree with most, though not sure how I feel about the counter-clockwise directional shorthand 🤔 I'd also never considered the cross-language implication of !important meaning the opposite in most languages!

Table layout should be sane.

This is also a small slice of history:

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.