Board Thread:Support Requests - Designing Your Wikia/@comment-7616725-20151107153601/@comment-5062941-20151107161222

Seems like this page can explain why Common.css won't work on your wiki's Oasis skin. Unless you don't want to go through the process of asking the staff, you need to add your font changes in Wikia.css for it to show up on Oasis skin, then you need to clear your cache again so you can see if it changed. :)