CSS Selector For Child Theme

Building a site right now, and I have a parent theme that I have built along with a child theme that is mostly just a CSS change, and a folder with a new image. Is there an easy way to build a CSS selector (similar to the ones in the BuddyPress themes)?

Just looking for some sample code, preferably without a lot of overhead. I do more front end stuff, and tend to get lost in to much php...

I know that I could just create another child theme, but I need to roll out about fifty sites, and a selector would be a little easier. (In my mind at least...)