Chrome: Stylebot lets you easily adjust the style sheets of nearly any page using a button-based control panel or editing the raw text of the style sheet. Most people will use this for mundane applications such as font changes and hiding ads, but using this powerful extension you can completely reskin sites and share your custom CSS with others using the developer's forum.
The Stylebot Social site has lots of CSS tweaks that can be implemented easily even if you don't know what CSS means. In the past hour I've used Stylebot to reskin Google Docs as MS Office, a create a cleaner version of iMDB, and gone back to the old YouTube page. I'm really looking forward to seeing what the Stylebot community comes up with in the future.
Privacy watchdogs take note:
The notice you see about having access to your website data, tabs and browsing activity is automatically generated because Stylebot runs on every tab. Stylebot doesn't try to look at or store any of your private data. Bookmark access is required for the sync feature, if you enable it.
Stylebot is a free extension available in the Chrome Web Store.
Stylebot [Chrome Web Store]