Board Thread:Support Requests - Designing Your Wiki/@comment-26020286-20170527212308/@comment-9605025-20170527223322

However, Fandom usually won't give you any trouble if you change it for yourself only. That can be done through personal CSS rather than site CSS.

Edit:

By the way, I took a look at the example you provided. It seems that the reason their header is different is because they use CSS that is too generic.