This is a documentation request first and foremost. There needs to be a CSS reference for all the containers, divs, elements, and common classes used to allow developers (and general users) to easily figure out how to override styles when the options are not available in the settings.
As an enhancement to the builder, it would be nice if there was a way, in the live editor (rendered content), to right-click and get the option to copy CSS and then paste CSS either to another element or into the custom CSS areas (page or global), or both elements and CSS area.
