I was hoping for something that could work for individual cards.

If you look at http://rigsomelight.com/devcards/#!/devdemos.defcard_api, you will see options for :frame and :padding and :classname. Between those, you can make any devcard look like anything.

To be more extreme, you can totally override all CSS with this: http://rigsomelight.com/devcards/#!/devdemos.css_opt_out

That way you can make it look like anything you want.