We need to document our reusable patterns of HTML/CSS so we don't repeat the same CSS over and over for each plugin/core component with specific selectors.

Totara has an element library plugin which is a good starting point, but needs to be expanded. This should document the current patterns/elements in Moodle 2.5 and list changes to those patterns/elements in releases.

This will greatly benefit themers as it will reduce the list of custom styles they have to override.

More reading:

http://www.stubbornella.org/content/2013/06/05/creating-living-style-guides-to-improve-performance/