I use pandoc to convert markdown to pdf+epub (https://learnbyexample.github.io/customizing-pandoc/). For web version, I use mdbook (https://github.com/rust-lang/mdBook) mainly because it comes with user choosable themes and search by default.

However, if I had to start from scratch, I'd probably look at Quarto (https://quarto.org/) or Mau (https://project-mau.github.io/index.html)