Board Thread:Support Requests - Designing Your Wiki/@comment-44745594-20200904005225/@comment-9605025-20200904032627

".page-Category_MyCategory" instead of ".page-MyPage". As described here, the body element of each page has a class of the form "page-*" where "*" is replaced by the full name (i.e. namespace and title) of the page slightly modified. The full name, from what I can tell, is modified by replacing any characters that are not a-z. A-Z. or 0-9 with underscores and then collapsing consecutive underscores into a single underscore.