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
More wording would definitely help because rules like `padding-left: 10px` when only modifying the left is usually what's preferred. Different developers will have different experience levels and won't be able to read generic rules and interpret them correctly. In that sense, writing a CSS style guide is much harder than writing a JS style guide because just by the nature of CSS you get into much more of the details.