Basic OnPaint and OnSizeChanged Methods for a Resizable Control

// after InitializeComponent()
this.ResizeRedraw = true; // If you want resizing to cause a redraw

protected override void OnSizeChanged(EventArgs e)
{
    base.OnSizeChanged(e);
    this.Invalidate();
}

protected override void OnPaint(PaintEventArgs pea)
{
    try
    {
        pea.Graphics.FillRectangle(Brushes.DarkOliveGreen, 
new Rectangle(0, 0, Width, Height));

        // Create a new pen.
        using (Pen pen = new Pen(Brushes.Black))
        {
            // Draw a line
            Point pt1 = new Point(ClientRectangle.Left, 
ClientRectangle.Bottom - 1);
            Point pt2 = new Point(ClientRectangle.Right, 
ClientRectangle.Bottom - 1);
            pea.Graphics.DrawLine(pen, pt1, pt2);
        }

    }
    catch (Exception ex)
    {
        //TODO: Log these errors.
    }
}