uxtheme: Use COLOR_BTNFACE to fill scroll bar background.

dlls/comctl32/tests/misc.c

@@ -888,8 +888,8 @@ static void test_themed_background(void)
         {WC_TREEVIEWA, 0, treeview_seq},
         {UPDOWN_CLASSA, 0, empty_seq},
         {WC_SCROLLBARA, 0, scrollbar_seq, TRUE},
-        {WC_SCROLLBARA, SBS_SIZEBOX, empty_seq, TRUE},
-        {WC_SCROLLBARA, SBS_SIZEGRIP, empty_seq, TRUE},
+        {WC_SCROLLBARA, SBS_SIZEBOX, empty_seq},
+        {WC_SCROLLBARA, SBS_SIZEGRIP, empty_seq},
     };
 
     uxtheme = LoadLibraryA("uxtheme.dll");

dlls/user32/tests/scroll.c

@@ -802,7 +802,6 @@ static void test_visual(void)
 
         hdc = GetDC(hwnd);
         color = GetPixel(hdc, 5, 5);
-        todo_wine_if(bThemeActive)
         ok(color == colors[1], "Expected color %#x, got %#x.\n", colors[1], color);
 
         ReleaseDC(hwnd, hdc);

dlls/uxtheme/scrollbar.c

@@ -62,8 +62,9 @@ void WINAPI UXTHEME_ScrollBarDraw(HWND hwnd, HDC dc, INT bar, enum SCROLL_HITTES
         else
             state = SZB_RIGHTALIGN;
 
-        if (IsThemeBackgroundPartiallyTransparent(theme, SBP_SIZEBOX, state))
-            DrawThemeParentBackground(hwnd, dc, NULL);
+        /* Tests show that COLOR_BTNFACE is used instead of DrawThemeParentBackground() for drawing
+         * background */
+        FillRect(dc, rect, GetSysColorBrush(COLOR_BTNFACE));
         DrawThemeBackground(theme, dc, SBP_SIZEBOX, state, rect, NULL);
     } else {
         int uppertrackstate, lowertrackstate, thumbstate;