It's strongly advised not to use your main account as a bot in a wiki. Instead, you should create another account to be used as a bot and contact the local bureaucrat in the wiki for approval. If you get approval from the bureaucrat, or if you are already a bureaucrat of the wiki, contact Fandom Staff to request the bot flag to the account.
should be placed in the wiki MediaWiki:Wikia.css. As I said, it should be imported at the very top of the CSS page since it is an import.
And all you need to do after that is to wait a few minutes to bypass cache and changes should be set.