I'm currently wading through Conf 2.6-dr1 main-action.css as part of the QA process for Theme Builder 3.0 - prior versions of our theme didn't include main-action.css but instead used a much trimmed-down version to reduce download times and make it easier for theme designers to add their own CSS without constantly "undoing" styles set by the main-action.css. However, With Confluence 2.6 and Builder 3.0 we decided to start using main-action.css again as it's now much cleaner.

There are however, some items that could be cleaned up and I will create sub-tasks to this issue to list them. This process will likely take me several days as there's a LOT of CSS in there hehe.