I can't seem to get any kind of ScrollbarRenderer from the ChatBox or the ChatBoxRenderer. I can get a RenderData object, but I can't make any use of it. Creating a ScrollbarRenderer, passing ChatBox->getRenderer()->getScrollbar() into its setData(), modifying the background texture, and using the modified ScrollbarRenderer's getData() for ChatBox->getRenderer()->setScrollbar() has no effect.
That was just a guess though, since guessing is the best I can do with no useful documentation or examples.
So what's the trick to getting access to a ChatBox ScrollbarRenderer?