The concept makes more sense for styling simple document style pages from 20 years ago, but it hasn't scaled to modern designs, complex web UIs and responsive pages that we want to code now, which isn't that surprising.

> we would all be writing purely semantic html with completely orthogonal and swappable css. And today literally no one designs web sites that way - html today is mostly specific to presentation

I think of HTML + CSS as the presentation layer now, and the data lives in your e.g. database and Markdown files, so the data and its presentation are still separate enough.

The idea of just swapping out the CSS to completely restyle a complex site is nice, but people need to accept this hasn't worked out (and not because devs are bad at CSS) and move on.