A single classless stylesheet that makes semantic HTML readable and tidy out of the box.

A mostly classless stylesheet by Kev Quirk that makes plain semantic HTML look tidy. It is about 10 KB, responsive, switches to a dark theme on its own and uses a local sans-serif font stack.
You add one stylesheet and write normal HTML; a few optional classes are there if you need them. The site says it suits simple sites like a personal blog, an about page, or the start of a new site.
It is MIT licensed, with a Getting Started guide on the GitHub wiki.