By default, XF comes with the following prefix styles: Creating custom styling using the Other, using custom CSS class name option is fairly straightforward. This guide will explain how to. The easiest way by far to add new prefix styling...
Hmmm
one of these addons are stopping it working.. isn't the custom theme/addons for it as I disabled it, yet it worked on a test installed of Xenforo with the custom theme installed (on default theme)