Removing theme media from the status bar

[so8...@gmail.com]

I have a custom firefox theme, and somehow it puts a light near-transparent gradient (with rounded corners) on the status bar. I'd like to remove it with userChrome.css but have no idea how. How can I mod the media on pentadactyl's status bar, and more importantly, where can I find docs about styling pentadactyl for cases like this in the future?

Thanks!