82 -  CSS style guide

A proposed style guide to cover CSS code commits to the jQuery projects.  Open to suggestion for rules, this pass is based on the CSS in jQuery Mobile and jQuery UI.

Based off of Issue https://github.com/jquery/contribute.jquery.org/issues/82
Okay, I was a little confused on this one, since I saw it done here: 

https://github.com/jquery/jquery-ui/blob/master/themes/base/button.css#L109

Although on that note, do we want to go into proper commenting at the top of a css file?