I do not know the whole picture, but if you are asking for blind one-shot CSS, you might benefit from wiring the model to take screenshots of various end-browsers and discuss them as you iterate.

Offering freelance estimates for CSS design changes before frameworks were around was a problem.

I actually have very detailed specifications around the CSS, the problem is that LLM's are trained mostly on codebases with high amounts of complexity so they like to create layer of abstractions that only make your codebase much harder to reason about, machine and man alike. This is very visible in CSS, where almost every single thing automatically becomes a component wrapping the CSS (be it React or LiveView in my case), which is very often meaningless because the CSS itself is the component.