Firefox has always had the edge when it comes to using custom CSS to customize web pages to look differently, but Google Chrome has caught up with Stylebot, an extension that lets you easily customize any element on any web page. And now they have downloadable styles too.
If you’re still not sure about how it all works, here’s a short video that explains creating a customization:
You can also check out Stylebot Social, where you can download styles for many specific web sites.
Stylebot [Google Chrome Extensions]