Board Thread:Support Requests - Designing Your Wiki/@comment-33281220-20181004215159/@comment-9605025-20181004231650

You question has a simple answer. You probably haven't done anything wrong. Wikia stopped supporting MonoBook and Uncyclopedia a long while back and removed them entirely in May. Now, the only skins supported are Oasis (for Desktop) and Mercury (for mobile; cannot be customized). If you want to know why they were removed, I suggest reading the following threads.

Thread:1456214

Thread:1456210