Incomplete list of mistakes in the design of CSS

I'd like to propose for the list:

Default heading styles should not have equal top and bottom margin. Headings should be closer to the content they label than to the content they are setting their content apart from.

h1, h2, h3 should not have different styles. it's an anti-pattern that leads to broken accessibility

moreover h* is just broken whenever dealing with more dynamic content — it simply can’t reasonably be made to work according to accessibility recommendations — and the accessibility guidelines around never skipping a level themselves are ridiculous given the practical reality that dynamic content exists and we have only h1, h2, etc. to work with — the readers and specs are what need to adapt here, not the entire internet

there should really be one header tag and its level should be based on some nesting depth

and don’t get me started on the maintainability mess that is z-index… better we have a system to centrally maintain an ordering list than a distributed one which only works reasonably consistently if you already know everything in the whole system