I recommend perusing the code. Since it’s in Nim it’s pretty approachable (and performant). There’s still lots of gnarly bits like implementing HTML DOM and web specs, but it doesn’t take you days to grasp the basic setup.
Chawan started out as a w3m clone, and the UI still resembles it. However, the architecture has turned out quite different, with pages loaded in separate processes, and protocol/file type handling separated out into external binaries. An interesting result is that you can even register decoders for custom inline image formats, although practical use cases of this are rather minimal.
There is a gallery showcasing some websites being rendered here: https://chawan.net/gallery/index.html
[1]: https://nim-lang.org