I'm doing some custom CSS for the tabs (you really need a better default styling for those) and I discovered
#ufc0 et al.
It was a bit of a surprise to me that after changing the fonts in the theme settings that many of the visual elements in the theme maintained the original fonts. I see that is because the custom CSS is referring to the font directly, rather than using something like #uff0, or creating custom font names like UpFrontFontOne, as noted in http://stackoverflow.com/questions/14259560/is-it-possible-to-specify-custom-name-for-a-google-font.
So have I just not seen the magic document that tells me how to do this, or do I need to make a feature request.