The largest part of the CSS is the styling of the navigation bar. I didn't find a way to create a pleasant and mostly normal looking navigation using unstyled HTML tags. Using such a small amount of CSS also removed the need for any CSS preprocessors like Sass.
When building files from sources, make (or mk) is a great general purpose solution. There's no reason I shouldn't reuse that tool and my knowledge about it when building static web sites. Writing a Makefile is done much faster than learning any of the existing static site builders, at least as long as you don't need 90% of their features.
Suggestions on how to add these in the most simple way are welcome!
See all the details in the source code at https://github.com/karlb/simplicity.