You should check out Radix UI (https://www.radix-ui.com/). Same idea as headless ui, but it doesn't assume that you will use Tailwind. I _think_ they add css classes to all of their components to allow you to choose any styling method you want, but I'm usually working with ShadCN (which is one level up and uses tailwind).

Though, I'll say that I agree with OP that a lot of functionality already exists within HTML and browsers.