Userstyles allow you to use the "Stylish" addon to apply custom CSS (GUI Colors, Background Colors, background Images, and other stuff.) to your website to have it appear like you want it to!
Once installed on your browser, you can use the link at the top to search for styles that other users have made for CL, or other websites. Among other things it can be used to make your own custom CL styles! Here's a few for example: