Specifically, everything about making Wikia look nice is broken, but there's other stuff too. Probably.
1) Wikia's CSS page is torture, something I learned the hard way when working out how to make custom tags. Typing "a.tag" like a normal human being causes Wikia to tell you it's over-qualified. What? It's the first thing I typed! How can the category possible already be defined? It also breaks out the apocalypse sirens when you use "!important", even though not using it causes everything you've typed to be completely ignored in favour of Wikia's standard skin. Because, y'know, I'm coding this all for the hell of it.
2) As Wikia itself will constantly (and I mean constantly tell you if you edit a lot), over half of readers are reading a wikia on mobile devices. It would only make sense, then, that over half of editors are editing from mobile devices? Clearly not. I have both an Android phone and an iPad, and editing from either is less preferable than 50000 volts pulsing straight through the reproductive organs, unless you get lucky and manage to tap the tiny little arrow next to the edit button which allows you to use the classic editor. It's the only one that works.
3) As mentioned before, Wikia seems to be obsessed with "making sure everything looks great to all visitors". This is easy enough when optimising the view for desktop (alongside desktop XL) and tablet, because there's not much difference - the only real contributing factors are the separation of text and the size of non-text objects. Lord help the majority of wikia-readers who are using a mobile reader, then, because no matter how hard you try, it will always look horrible on a page-reader. Maybe if Wikia had any idea how painful the process was, it'd stop nagging me.
4) Wordmarks and favicons are hell to upload. Wordmarks have to be a 255x65 (or smaller) .png file, for reasons I assume to have to do with transparency. Fair enough, you're thinking, it doesn't want to be jarring. The trouble here is that the "over 50%" that Wikia is constantly trying to force us to babysit are, even as admins, powerless to change the wordmark from the standard text, because a) for some reason you can't upload a file that's already stored on the wikia as a wordmark even though that'd make the most sense, and b) you can't get around this by saving the file to your mobile, because most, if not all, mobile devices save all pictures as .jpg, no matter what form it was in before.
5) Not only do favicons also have to be transparent, they have to be 16x16 (which is absolutely tiny) and .ico files. Who, besides website designers, has ever heard of an .ico file? So, after getting it all transparent in paint.net, I'm forced to go online to convert my .png to an .ico, which is a) just awkward for a website that's all about making it easy for users to contribute, and b) will most likely result in my PC getting a virus in the process.
Sort it out, Wikia, I could go on ranting for years.
P.S. Also I uploaded a wordmark and changed the favicon... yay.