Resize shapes in C#

Question

How can I resize a rectangle with Mouse_down and Mouse_move event in C# ?

I drew 2 rectangles and I want to resize them with the corners. (The left top corner is because of the moving.) The blue rectangle have to contain the red one.

That's my code:

namespace __RajzAlap
{
    public partial class Form1 : Form
    {
        Graphics g;

        Pen bluePen = new Pen(Color.Blue, 2);
        Pen redPen = new Pen(Color.Red, 2);
        PointF balfont = new PointF(100, 100);
        PointF balfont2 = new PointF(120, 120);
        int meret1 = 300;
        int meret2 = 30;
        int megfogva = -1;
        float s = 5;      

        public Form1()
        {
            InitializeComponent();

            
        }

        private void canvas_Paint(object sender, PaintEventArgs e)
        {
            g = e.Graphics;

            Rectangle kekTeglalap = new Rectangle((int)balfont.X, (int)balfont.Y, meret1, meret1);
            Rectangle pirosTeglalap = new Rectangle((int)balfont2.X, (int)balfont2.Y, meret2, meret2);

            g.DrawRectangle(bluePen, kekTeglalap);
            g.DrawRectangle(redPen, pirosTeglalap);

            //sarkok rajzolása
            g.FillRectangle(new SolidBrush(Color.Blue), balfont.X - s, balfont.Y - s, 2 * s, 2 * s);
            g.FillRectangle(new SolidBrush(Color.Blue), balfont.X + meret1 - s, balfont.Y + meret1 - s, 2 * s, 2 * s);
            g.FillRectangle(new SolidBrush(Color.Blue), balfont.X + meret1 - s, balfont.Y - s, 2 * s, 2 * s);
            g.FillRectangle(new SolidBrush(Color.Blue), balfont.X - s, balfont.Y + meret1 - s, 2 * s, 2 * s);
            g.FillRectangle(new SolidBrush(Color.Red), balfont2.X - s, balfont2.Y - s, 2 * s, 2 * s);
            g.FillRectangle(new SolidBrush(Color.Red), balfont2.X + meret2 - s, balfont2.Y - s, 2 * s, 2 * s);
            g.FillRectangle(new SolidBrush(Color.Red), balfont2.X - s, balfont2.Y + meret2 - s, 2 * s, 2 * s);
            g.FillRectangle(new SolidBrush(Color.Red), balfont2.X + meret2 - s, balfont2.Y + meret2 - s, 2 * s, 2 * s);

        }

        #region Mouse handling
        private void canvas_MouseDown(object sender, MouseEventArgs e)
        {

            //bal felső sarok mozgatás
            if (Megfogva(balfont, e.Location, s)) megfogva = 0;
            else if (Megfogva(balfont2, e.Location, s)) megfogva = 1;

           
        }
        private void canvas_MouseMove(object sender, MouseEventArgs e)
        {

            //bal felső sarok mozgatás
            if (megfogva != -1)
            {
                switch (megfogva)
                {
                    case 0: balfont = e.Location; break;
                    case 1: balfont2 = e.Location; break;
                    default: break;
                }
                canvas.Refresh();
            }        
           
        }
        private void canvas_MouseUp(object sender, MouseEventArgs e)
        {
            megfogva = -1;
        }
        private void canvas_MouseWheel(object sender, MouseEventArgs e)
        {

        }
        #endregion

        //bal felső sarok mozgatáa
        private bool Megfogva(PointF p, PointF eger, float tavolsag)
        {
            return Math.Abs(p.X - eger.X) <= tavolsag &&
                   Math.Abs(p.Y - eger.Y) <= tavolsag;
        }
    }
}