ComboBox items / popup

Hello all.

When changing the LookAndFeel for ComboBox, I found that changing the font only changes the selected entry, and that the selection is made from a Popup menu, rather than the ComboBox. My question is, how do I change the Popup menu from the ComboBox? I can’t see a method to get the popup menu from the ComboBox. Even if I did, I can’t see the option to change individual entries in the Popup menus. If this is the case, how best to do this, and how also to change the font of the headers?

Thank you.