Resize borderless panel on winform

Question

Hi i have a borderless form that i want to be able to resize, searching here i found this code

public partial class Form1 : Form {
public Form1() {
  InitializeComponent();
  this.FormBorderStyle = FormBorderStyle.None; // no borders
  this.DoubleBuffered = true;
  this.SetStyle(ControlStyles.ResizeRedraw, true); // this is to avoid visual artifacts
}

protected override void OnPaint(PaintEventArgs e) // you can safely omit this method if you want
{
    e.Graphics.FillRectangle(Brushes.Green, Top);
    e.Graphics.FillRectangle(Brushes.Green, Left);
    e.Graphics.FillRectangle(Brushes.Green, Right);
    e.Graphics.FillRectangle(Brushes.Green, Bottom);
}

private const int
    HTLEFT = 10,
    HTRIGHT = 11,
    HTTOP = 12,
    HTTOPLEFT = 13,
    HTTOPRIGHT = 14,
    HTBOTTOM = 15,
    HTBOTTOMLEFT = 16,
    HTBOTTOMRIGHT = 17;

const int _ = 10; // you can rename this variable if you like

Rectangle Top { get { return new Rectangle(0, 0, this.ClientSize.Width, _); } }
Rectangle Left { get { return new Rectangle(0, 0, _, this.ClientSize.Height); } }
Rectangle Bottom { get { return new Rectangle(0, this.ClientSize.Height - _, this.ClientSize.Width, _); } }
Rectangle Right { get { return new Rectangle(this.ClientSize.Width - _, 0, _, this.ClientSize.Height); } }

Rectangle TopLeft { get { return new Rectangle(0, 0, _, _); } }
Rectangle TopRight { get { return new Rectangle(this.ClientSize.Width - _, 0, _, _); } }
Rectangle BottomLeft { get { return new Rectangle(0, this.ClientSize.Height - _, _, _); } }
Rectangle BottomRight { get { return new Rectangle(this.ClientSize.Width - _, this.ClientSize.Height - _, _, _); } }


protected override void WndProc(ref Message message)
{
    base.WndProc(ref message);

    if (message.Msg == 0x84) // WM_NCHITTEST
    {
        var cursor = this.PointToClient(Cursor.Position);

        if (TopLeft.Contains(cursor)) message.Result = (IntPtr)HTTOPLEFT;
   else if (TopRight.Contains(cursor)) message.Result = (IntPtr)HTTOPRIGHT;
   else if (BottomLeft.Contains(cursor)) message.Result = (IntPtr)HTBOTTOMLEFT;
   else if (BottomRight.Contains(cursor)) message.Result = (IntPtr)HTBOTTOMRIGHT;

   else if (Top.Contains(cursor)) message.Result = (IntPtr)HTTOP;
   else if (Left.Contains(cursor)) message.Result = (IntPtr)HTLEFT;
   else if (Right.Contains(cursor)) message.Result = (IntPtr)HTRIGHT;
   else if (Bottom.Contains(cursor)) message.Result = (IntPtr)HTBOTTOM;
    }
}}

I was able to make it work on my form in every direction except on top because i have a panel. How can i modify the code to make it work also for the top? Thx