I'm not really into LaTeX but I am really into the specific problem of authoring documents with a certain (user-defined) look-and-feel by leveraging some (very user-friendly) DSL that is close to markdown but with more features

Does Typst support themes so that I can achieve that? Are there other tools I should be aware of?

Are there tools that do all of the above and have themes defined as CSS?

I'm aware of RMarkdown + Knitr which is a fantastic combo (and honestly my inspiration for digging into this problem) but that's obviously still too much "programming" for wider adoption