C#winform btnボタンの外枠を取り除く

    class newbtn : System.Windows.Forms.Button //   
    {
        protected override void OnPaint(PaintEventArgs e)
        {// 

            base.OnPaint(e);
            System.Drawing.Pen pen = new Pen(this.BackColor, 3);
            e.Graphics.DrawRectangle(pen, 0, 0, this.Width, this.Height);// 
            pen.Dispose();

        }
    }