User blog comment:DaNASCAT/Technical Update: June 14, 2011/@comment-3388044-20110615053706/@comment-1066636-20110616081228

While I understand the reasoning behind not including Common.css when Oasis was originally released, I think it's rather impractical in the long run. There's now no place to store CSS for things like templates which affect all skins, and duplicating CSS between Wikia.css and Common.css is a bit of a pain.

And yes, I do know that this can be solved with an, but requiring that level of CSS knowledge when one of the goals of Oasis is to improve usability doesn't quite match up, to be honest.

Not that Wikia is going to listen; I guess I just like talking to walls ;-)