I'm having some trouble coming up with an appropriate starting point to get the List that drops down out of the ComboBox to style. So I've extended/bound the TriggerFieldDefaultAppearance and it looks good. Further, I have gotten my other ListViews to style by extending ListViewCustomAppearance, creating my own ListViewDefaultStyle and then passing that into the constructor.
I'm just not sure how I would go about creating or binding a ListViewAppearance to the List that drops down in the ComboBox. How are other people handling this piece?
The ListView can be provided as a parameter if you create the ComboBoxCell yourself. This allows you to customize it any way you choose, including a custom cell (in the listview that is), or a custom appearance.
That said, if you are using any custom appearance everywhere, don't forget to set it as a rebind rule in your module (or in another module just for theming) with replace-with. This will automatically have GWT use your appearance instead of a built-in appearance.