static extern bool GetTitleBarInfo(IntPtr hwnd, ref TITLEBARINFO pti);

See structure: [TITLEBARINFO]

    GETTITLEBARINFOEX = 0x033F,

struct TITLEBARINFO

Structure TITLEBARINFO

        public    struct TITLEBARINFO

        public static extern bool GetTitleBarInfo(IntPtr hwnd, ref TITLEBARINFO pti);

    Win32.TITLEBARINFO pti = new Win32.TITLEBARINFO();

    bool result = Win32.GetTitleBarInfo(Handle, ref pti);