Function HitTestThemeBackground 

pub unsafe extern "system" fn HitTestThemeBackground(
    hTheme: HTHEME,
    hdc: HDC,
    iPartId: c_int,
    iStateId: c_int,
    dwOptions: DWORD,
    pRect: LPCRECT,
    hrgn: HRGN,
    ptTest: POINT,
    pwHitTestCode: *mut WORD,
) -> HRESULT