dotcss is two things:
1. A tiny web server that runs on your machine, serving CSS files out of ~/.css
2. A Chrome extension that fetches these CSS files and injects them based on their filename.
This one is the Chrome extension.
The files are requested on a per-page basics, based on the hostname. For example, if you go to https://github.com, ~/.css/github.com.css would be injected into the page.
This makes it super simple and easy to change and improve the look of your favorite sites.
You can get the server component of dotcss at https://github.com/stewart/dotcss