Board Thread:New Features/@comment-4079189-20150913022714/@comment-4731443-20150913202815

Well, you do already get three levels of specificity:
 * 1) .portable-infobox to alter all infoboxes
 * 2) .portable-infobox.pi-theme-your-theme through theme for a different model
 * 3) .portable-infobox.pi-theme-your-other-theme through theme-source for even more refined details

If you need more than that, I think what is needed is inline CSS or just the ability to define as many classes as we want rather than use some made-up attributes. Making more and more theme/theme-source equivalents to accommodate various use cases seems a silly way to achieve the flexibility we already had with wikitext templates.