https://bugs.winehq.org/show_bug.cgi?id=44522
--- Comment #2 from Nikolay Sivov bunglehead@gmail.com --- Window frame and other non-client parts don't support theming as of today. I'm not sure how it works exactly, but it's possible hooking user32 to use uxtheme directly, or duplicating useful parts in user32 could be an option. Window scrollbars theming is the same issue.