dotcss is a Google Chrome extension that executes css files in ~/.css based on their filename.
If you navigate to http://www.google.com/, dotcss will execute ~/.css/google.com.css.
This makes it super easy to spruce up your favorite pages using css.
See https://github.com/marksands/dotcss for full installation instructions. You need to run a server in addition to this Chrome extension.
Only works on OS X.