Board Thread:Support Requests - Designing Your Wikia/@comment-25062343-20160523094746/@comment-9605025-20160604220645

Okay, I'm not too familiar with the portable infoboxes, but I think what you are looking for is here (Help:Infoboxes/CSS). I know with the classic infoboxes, you could just put it in the infobox markup itself. It looks like the portable infoboxes require you to edit the wiki's css. I would suggest using "theme-source" so that you only need to create one template rather than a separate template for each group.