Board Thread:Support Requests - Designing Your Wiki/@comment-3032314-20130309023813/@comment-10688548-20130309035243

Firefox has a "Style Editor" that allows you to see all the CSS sheets currently affecting your document, and allows you to on-the-fly change existing ones and add new ones. You can find it at Shift-F7 (or in Tools > Web Developer). Similar things exist for other browsers I'm sure, probably in the form of extensions.