Is CSS that awesome? It's still a language designed for styling webpages with 30 year of added features. I'd argue something purpose built would be a much better tool for the potential usecases people try to use CSS for now.

I guess I am asking, if modern CSS is so awesome, it's awesome compared to what exactly?

I'm asking the same question!

No doubt the very loudly opinionated not-web-dev community, who have So Much To Say about web devs and web tech, have produced an uncontroversial, perfect layout system, styling system, and language to produce the replacement for this awful web tech. Where is it? What is it? Please provide (the better version of) a hyperlink to the docs.

I think the argument lies in its flexibility and versatility (regardless of it being the most efficient or effective tool for this one particular task).

Duct tape is awesome for the same reason -- even though there are several effective use cases for duct tape where a different tool would technically be "better" for the job.

I was writing CSS +20 years ago and it's never been better.

What kind of system would you propose (or do you envision) for applying visual styling to HTML markup in modern web pages today?

You can keep it high level but your comment makes me think you have something in mind, and I'm honestly curious.

compared to old css, it just keeps getting better

People keep reinventing 'better' styling tools, and we ends up with more bloat and more magic, while static UIs definately stay simpel.