Is there any reason you're not just using shadow DOM?

Afaik that doesn’t solve the problem of global CSS. Whatever framework I use to build the application itself (right now I’m using Tailwind), I don’t want to risk it polluting the canvas itself.

edit: I'd never spent much time looking at shadow dom, but it does appear that you can encapsulate styles with a shadow root. Had no idea - that's really interesting, thanks!