Board Thread:Support Requests - Designing Your Wikia/@comment-25631483-20150826230210/@comment-4731443-20150827020102

For now this isn't really possible within the template, and a little complicated using external CSS. You can style elements inside the tags normally (for example,  will produce a white link), but in the case of a background color, you'll see that doing something like this doesn't fill the entire row, but only the area occupied by the text itself.

For that you would need to use CSS linked to your infobox class. First, I recommend reading Help:PortableInfoboxes/CSS if you haven't already. Then you can use a statement similar to this in your wiki's Special:CSS: .pi-theme-YOUR_CLASS div:nth-of-type(1) div:first-of-type { background-color: #000000; } Replace:
 * .pi-theme-YOUR_CLASS to use the class defined in your infobox's theme attribute
 * div:nth-of-type(1) so that the number matches the row you want to affect; counting begins at the first row that is not the title or main image, also skipping any tags if used
 * The actual color in the background-color to what you want to use

Let me know if you need more details :)