I realize in retrospect OP was asking about Compose HTML docs, not Kobweb docs, whoops!
Yeah, their docs story is really not that great. However, you can get a good feel for most of what Compose HTML offers by reading through all of their tutorials, which you can find here:
https://github.com/JetBrains/compose-multiplatform/tree/master/tutorials/HTML
That said, once you get a feel for how HTML / CSS translates to Compose HTML in one way, you kind of know almost the whole thing.