Honestly, I think that considering a good css approach for a setup like this does make sense. I think the key question now is how do we ensure that this all gets usable for non-technical people.
Most people won't know how to start prompting AI to use an existing stylesheet, even when they can vibe it together. But the next step is providing something where it all "works" out of the box.
I really tried to write this post to get non-programmers in with the start, and provide some ideas to programmers at the end.
