Board Thread:Ask the Staff/@comment-5250721-20161025055005

I've typically done a lot of the coding for the other wikis I've worked on, but can someone help clarify for me what the difference is between a Wikia's Common.css and regular Wikia.css? Because from what I've seen, they each function in a similar way, but sometimes certain commands don't work on one page, so the other works. And how would we know when to use each page?  