I’ve made some gnarly custom forms over the years but never quite run into the problem you’re describing.

These days if starting a greenfield web app, each page has its own style/css sent in the head tag.

Because it’s usually just base layout + page specific styles/overrides then it barely adds any overhead in the scheme of things(couple of extra KB).

Maybe the base layout could be moved into a static file to be cached but whatever, it’s already ridiculously quick to render plain html/css.