Sorry, I though you're just referring to the firefox concept.
Anyway, just view your youtube profile/channel and click Themes and Colors.
After selecting it. Click show advanced options.
You'll see the styles and configuration after click ^.
Modify the CSS, background, font, so-on.
e.g. the css idea isn't for Firefox only.
Last edited by Ephemeral (2010-09-02 04:37:15)