void DrawToggleButton(Graphics g)
        {
            VisualStyleRenderer glyphRender = null;
            if (IsCollapsed)
                glyphRender = new VisualStyleRenderer(VisualStyleElement.TreeView.Glyph.Closed);
            else
                glyphRender = new VisualStyleRenderer(VisualStyleElement.TreeView.Glyph.Opened);
            glyphRender.DrawBackground(g, m_toggleRect);
        }

        void DrawToggleButton(Graphics g)
        {
            if (Application.RenderWithVisualStyles)
            {
                VisualStyleRenderer glyphRender = null;
                if (IsCollapsed)
                    glyphRender = new VisualStyleRenderer(VisualStyleElement.TreeView.Glyph.Closed);
                else
                    glyphRender = new VisualStyleRenderer(VisualStyleElement.TreeView.Glyph.Opened);
                glyphRender.DrawBackground(g, m_toggleRect);
            }
            else
            {
                if (IsCollapsed)
                    g.DrawImage(PlusImage, m_toggleRect);
                else
                    g.DrawImage(MinusImage, m_toggleRect);
            }
        }

void ResizeParent()
{
   int deltaHeight = this.FullHeight - m_collapsedHeight;
   this.ResizeParent(this.Parent, !this.Collapsed, deltaHeight);
}

void ResizeParent(Control control, bool collapsed, int deltaHeight)
{
   if (control != null)
   {
      this.ResizeParent(control.Parent, collapsed, deltaHeight);

      foreach (Control c in control.Controls)
      {
         if ((c.Anchor & AnchorStyles.Bottom) != 0)
            continue;

         Point p = c.Location;
         if (p.Y <= this.Location.Y)
            continue;

         if (collapsed)
            p.Y -= deltaHeight;
         else
            p.Y += deltaHeight;
         c.Location = p;                    
      }

      Size s = control.Size;
      if (collapsed)
         s.Height -= deltaHeight;
      else
         s.Height += deltaHeight;
      control.Size = s;
   }
}


void ToggleCollapsed()
{
   this.ResizeParent();
   this.Collapsed = !this.Collapsed;
   if (this.CollapseBoxClickedEvent != null)
      this.CollapseBoxClickedEvent(this);
}

Brush lBrush = new SolidBrush( BackColor );
g.FillRectangle( lBrush, i_textPos, bounds.Y, i_endPos - i_textPos, 2 );

SystemPens.FromSystemColor(Parent.BackColor)

    /// 

    /// CollapsibleGroupBoxDesigner is an control designer for the that 
    /// CollapsibleGroupBox. Allows mouse clicks on the collapse button. 
    /// 
summary
    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
    public class CollapsibleGroupBoxDesigner : System.Windows.Forms.Design.ParentControlDesigner
    {
        // This boolean state reflects whether the mouse is over the control.
        protected override  bool  GetHitTest(Point point)
        {
            CollapsibleGroupBox me = this.Control as CollapsibleGroupBox;

            if (me.m_toggleRect.Contains(me.PointToClient(point)))
            {
                // we can handle that; user clicked on toggle box.
                return true;
            }
            //Nope not interested
            return false;
        }
    }

    /// 

    /// GroupBox control that provides functionality to 
    /// allow it to be collapsed.
    /// 
summary
    [ToolboxBitmap(typeof(CollapsibleGroupBox))]
    [DesignerAttribute(typeof(CollapsibleGroupBoxDesigner))]
    public partial class CollapsibleGroupBox : GroupBox
    {

        ....
        public Rectangle m_toggleRect = new Rectangle(8, 2, 11, 11); // not private
        ....

        /// summary
        /// Save the size if control is collapsed. VS will serialize the attribute for us. 
        /// It is also shown in properties.
        /// 
summary
        [DefaultValue(false), Browsable(true), DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
        public Size FullSize
        {
            get
            {
                return m_FullSize;
            }
            set
            {
                m_FullSize = value;
            }
        }

g.DrawLine(SystemPens.Control, i_textPos, bounds.Y, i_endPos, bounds.Y);

g.FillRectangle(new SolidBrush(this.BackColor), 8, 2, i_endPos-8, 12);

using (SolidBrush drawBrush = new SolidBrush(Color.FromArgb(0, 70, 213)))
        g.DrawString(Text, this.Font, drawBrush, i_textPos, 0);

using (SolidBrush drawBrush = new SolidBrush(this.ForeColor))
				g.DrawString(Text, this.Font, drawBrush, i_textPos, 0);

void DrawToggleButton(Graphics g)
{
	g.FillRectangle(new SolidBrush(bmasmenos),m_toggleRect);
	g.DrawRectangle(new Pen(masmenos),m_toggleRect.Left+1,m_toggleRect.Top+1,8,8);
	g.DrawLine(new Pen(masmenos),m_toggleRect.Left+3,m_toggleRect.Bottom-6,m_toggleRect.Right-4,m_toggleRect.Bottom-6);
	if(IsCollapsed)
		g.DrawLine(new Pen(masmenos),m_toggleRect.Left+5,m_toggleRect.Top+3,m_toggleRect.Left+5,m_toggleRect.Bottom-4);
}

public Color BorderColor
{
	get{return m_borderColor;}
	set{m_borderColor=value;this.Invalidate();}
}