Sorry, I’m not being clear enough. I’m already using style.css, but I’m finding that overriding the #nav rules in default.css more complicated than its worth.
What I’d like to do is override default.css in the theme with a local copy so I can comment out the section which is causing me problems and replace it with fresh rules in style.css.
This is more a WordPress question than a Buddypress one, but is it possible to get WordPress to load a theme css file by placing a copy in your child theme, or do I need to mess with the PHP to change the location? In the interests of BC and upgradablility I’d rather not trash all the CSS.