Abstractions are great, as long as you understand their performance implications. Some are essentially free, some are surprisingly costly if you hold them wrong.

Sadly, there's no way around understanding HTML and CSS when you need to troubleshoot what a high-level framework built for you. (Or maybe there is! Render everything using WebGL, the way Flutter does, and Flash did before it. But it's a different kettle of fish.)

Open the browsers dev tools and you see HTML. Read MDN and you see HTML. Constantly translating back and forth between that and another language isn't worth it.

It's quite important for accessibility.

That's not the same because the abstraction a mature computer language provides is nearly complete (not totally complete, of course, but the situations where you ought to go digging through machine code or lower are pretty rare).

Outside of games, almost all the frameworks people use don't try to do that -- you are essentially trying to write HTML, but using the syntax of a different language, or each HTML thing in a thing from a different language. (Flutter is the exception -- it really does try to provide a complete abstraction, though it's certainly not without its tradeoffs.)

problem is, the most important "abstractions" for describing the UI are not built "on top of" HTML, but along side it (CSS and to a limited degree JS). the relationship between contemporary "frameworks" and HTML is not like that of C and assembler or even Rust and assembler. It is more like that of a driver of a vehicle that has each of a gasoline, electric and steam powered motor, and must constantly pick which one to use for a given situation (sometimes two and occasionally all three).