Would anyone be kind enough to save me a lot of checking, and tell me which menu files other than quantity_menu.xml use generic_background.xml ?

button_long.xml, button_short.xml and horiz_floating_scroll.xml from the looks of it.

Depends on the UI mod you're using, DarNifiedUI changes pretty much all of the "generic_background.xml" uses to a smaller "generic_background75.xml" or "generic_background50.xml". In vanilla Oblivion there are alot of menus using it, pretty much any menu that has some sort of background. What is it you are trying to do?

Thanks for the replies. Seem to have a handle on it now.