Welcome to userstyles.org, the largest collection of user styles anywhere! User styles let you change the way websites look. We've got Facebook themes, Tumblr themes, Google themes, Firefox themes, and more. There are tens of thousands of user styles, I'm sure you'll like at least a few.
The easiest way to use user styles is to use Stylish for Firefox or Stylish for Chrome. It's all free, by the way.
If you have Stylish already, or if you want to take a look around first, check out the styles below, try a search on the left, or browse by category.