Stuck with editing CSS

I'm customising m cPanel skin which will be the default skin for my clients but I cannot find out how to edit the CSS.

When I click Edit-Styles, I just get "/unprotected/broken.css" and no CSS to edit.

What am I meant to do? Am I meant to edit the .css file directly on the server, if so which is the correct one to edit?

Thanks.

 

Ignore this, I've answered my own question!