Yes, HTML & CSS alone won't replace JS. Of course, for complicated form validation HTML is not sufficient. But IMHO it's very important to provide basic functionality in HTML / CSS as much as possible / reasonable. Moving the functionality to HTML / CSS can potentially improve the SEO.

As for positioning, there is an experimental feature @position-try. Here I made a small demo where it handles overflows.

https://waspdev.com/articles/2025-06-29/css-features-web-dev...

But yeah, that's kind of limited if you need nice animations or some other complicated thing. Although it's fun.