IDLE uses the pre-ttk widget set and is indeed ugly.
See https://tkdocs.com/tutorial/idle.html for a case-study involving IDLE (Search for "Another Example" to see the settings window). You should be able to tell from the windows and mac screenshots how old this article is.
Those combo boxes are definitely not native. The menus are also off (the menu items are shorter and they turn blue instead of gray when highlighted).