GhostWire ComboBox - Skinning
You generally would not be making skins for the ComboBox. The component reuses the ListBox component, which in turn reuses the ScrollPane component which uses the ScrollBar component (you can see how efficient this is!).

Since the ScrollBar is truly skinnable, you can make scrollbars that look exactly the way you want.

After making your own scrollbar, you can proceed to make a ScrollPane component that uses the new scrollbar.

The "bot_mc" that you create when making the skin for the ScrollBar should be reused in the skinning for the ComboBox. The "arrow_mc" in the ComboBox component is actually an instance of the "bot_mc" in the ScrollBar component.