Thanks, Yana! That takes care of the issue with the oversized div. As a note to anyone who finds this thread in their own scenario... if you have a treeview in your panel bar item and you want horizontal scrolling to be handled by the panelbar, you need to disable the scrolling of the treeview. Otherwise, if the horizontal space is too small, the treeview horizontal scrollbar will appear, not the panel bar's. This would be ok, except for the fact that, if the treeview list is longer than the vertical space allowed, then the panelbar's vertical scrollbar will be shown and you will have to scroll all the way to the bottom to see the treeview's horizontal scrollbar. This is not ideal.
So, in my app I found that, to disable the scrolling of the treeview, I added the following to the treeview declaration:
I would have thought that setting the overflow to "auto" or "hidden" woudl have been more intuitive, but neither of those got the desired result of the panel bar's own horizontal scrollbar being displayed when the treeview content was too waide.