Skinning Gmail with a Custom Stylesheet

Short Version

• Install the URLid Mozilla/Firefox extension.
• Download this CSS file.
• Locate your profile folder and the chrome folder within that.
• Copy the downloaded CSS file to the chrome folder and rename it to userContent.css (if you already have such a file, you will have to merge the two).
• Restart Firefox.
• Visit Gmail.

Very nice hack, if you are bored from your Gmail Interface

[Origianl Article]