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
Maybe refer to them as "hyphens" rather than "dashes" because "dashes" can be ambiguous ("-" or "–" or "—").