Why GTK window has a wide border?

Found GTK window is not friendly for the screenshot on windows, why GTK window has a wide border default(entire image, just want to capture the red rectangle area)?

Hello! It’s a known issue on Windows. See https://gitlab.gnome.org/GNOME/gtk/-/issues/3136 and https://gitlab.gnome.org/GNOME/gtk/-/issues/3629 for details.