BuddyPress.org

Any css you put in custom.css overrides *all* css. Unless groups css is being loaded after custom.css and in that case it’s a bug and should be reported in trac. Don’t think it is though.

Example:

ul#group-list li, ul#member-list li, ul#blog-list li, ul#comment-list li, ul.item-list li { background: url(../images/message_thread_back.gif) top left repeat-x;}

That’s in ../member-themes/buddypress-member/css/groups.css. In your custom.css file you can change the ‘message_thread_back.gif’ to something else by overriding it in custom.css

ul#group-list li, ul#member-list li, ul#blog-list li, ul#comment-list li, ul.item-list li { background: url(../images/my_fav_message_thread_back.gif) top left repeat-x;}

This what you need?