I chose to use InDesign to typeset my self-published book, and I have to say the quality it produces from just placing some imported text with no other changes looks 1000 times better than this. It's easy to go down a rabbit hole and start really tweaking the layout but if all you're doing is applying some CSS anyway then you can produce better output with InDesign's defaults in about 5 minutes. I've been writing the book in Google Docs and printing chapters for review as I go, and it's nice to see a physical copy of your work. But I was blown away when I made my first PDF copy with InDesign how much better the typesetting is. It really does feel like a proper book and not an essay that I printed out for a school assignment.