What CSS needs (opinion, caveat, really far away in advanced features) is:

- A way to get values from sliders (type="range") (and style and modify them easily). Really, a way to get "value" from any <input> element.

- A way to have radio / checkboxes or labels inside labels work for multiple choices (or something other than making enormous arrays of radio selections and CSS choices)

- A way to have indexed arrays of numbers / choices (other than using a crazy complicated animation timing trick)

- String concatenation thats not so incredibly finicky and difficult to implement correctly

- Some way to retain the final "state" of a condition without resorting to playing an animation on "forwards" mode. Also, related, some way to not require the hidden checkbox hack everywhere.

- (Advanced, lower priority) A way to force var() calculation and optimizations other than making a zillion @property statements. "This expensive trig calculation is used a hundred times later on, better make it a separate ... nvm, it gets regex placed into every other calculation on the entire page ... " ¯\_(-_')_/¯

- If() and Function() ... wait, /inappropriate_swear, we're actually getting these after a quarter century.