(not affiliated, just a happy user)

It's paid, but if you want to deeply learn CSS interactively, I can't recommend this course enough:

https://css-for-js.dev/

Not just the best CSS resource I've encountered, but one of the best examples of interactive pedagogy period I've encountered.

The author also has lots of free resources if you want to get a flavor of the style:

https://www.joshwcomeau.com/tutorials/css/