Esme Povirk (@madewokherd) commented about dlls/comdlg32/navbar.c:
+ PAINTSTRUCT ps; + HDC hdc = BeginPaint(hwnd, &ps); + RECT rc; + HBRUSH old_brush; + HBRUSH bg_brush = GetSysColorBrush(COLOR_BTNFACE); + HBRUSH frame_brush = GetSysColorBrush(COLOR_3DSHADOW); + + GetClientRect(hwnd, &rc); + + /* clear background to avoid border trailing when resizing */ + FillRect(hdc, &rc, bg_brush); + + /* draw the 1px frame */ + FrameRect(hdc, &rc, frame_brush); + + /* erase the left border, retaining the top and bottom pixels */ I think you could remove the need for this by drawing the left border outside the window.
-- https://gitlab.winehq.org/wine/wine/-/merge_requests/1857#note_20173