C#

[StructLayout(LayoutKind.Sequential)]
private struct RECT
{
   public int Left;
   public int Top;
   public int Right;
   public int Bottom;
}

enum WM_MESSAGE
{
   WM_NCCALCSIZE = 131,
   WM_NCPAINT = 133,
   WM_NCHITTEST = 132,
   WM_NCLBUTTONDOWN = 161,
}

[StructLayout(LayoutKind.Sequential)]
struct NCCALCSIZE_PARAMS
{
   public RECT rgrc0, rgrc1, rgrc2;
   public IntPtr lppos;
}

[DllImport("User32.dll")]
private extern static IntPtr GetWindowDC( IntPtr hWnd );

[DllImport("User32.dll")]
private extern static int ReleaseDC( IntPtr hWnd, IntPtr hDC );

private Rectangle _rcButton = Rectangle.Empty;

protected override void WndProc(ref Message m)
{
   switch (m.Msg)
   {
      case (int)WM_MESSAGE.WM_NCCALCSIZE :
         if (m.WParam == IntPtr.Zero)
         {
             // shrink the client area
             NCCALCSIZE_PARAMS csp;
             csp = (NCCALCSIZE_PARAMS)Marshal.PtrToStructure(m.LParam, typeof(NCCALCSIZE_PARAMS));
             csp.rgrc0.Left += 1;
             csp.rgrc0.Top += 5;
             csp.rgrc0.Right -= 1;
             csp.rgrc0.Bottom -= 1;
             Marshal.StructureToPtr( csp, m.LParam, false );
         }
         break;

      case (int)WM_MESSAGE.WM_NCPAINT :
      {
         // draw the borders in the non client area
         IntPtr hDC = GetWindowDC(m.HWnd);
         Graphics g = Graphics.FromHdc(hDC);
         g.FillRectangle(SystemBrushes.Highlight, 0, 0, this.Width, 5); // top
         g.FillRectangle(SystemBrushes.Highlight, 0, 0, 1, this.Height); // left
         g.FillRectangle(SystemBrushes.Highlight, this.Width-1, 0, 1, this.Height); // right
         g.FillRectangle(SystemBrushes.Highlight, 0, this.Height-1, this.Width, 1); // bottom
         ReleaseDC( m.HWnd, hDC );
         break;
      }
   }

   base.WndProc(ref m);
}

//classes to inherit
public class widgetA
{
  public object wa;
}
public class widgetB
{
  public object wb;
}
public class widgetC
{
  public object wb;
}

//users class
public class AllWidgets: widgetA,widgetB,widgetC
{
  public AllWidgets(object a, object b, object c)
  {
  //constructor stuff here (i.e. this.wa = a; etc)
  }
}

//class usage
public void CodeFunction()
{
  AllWidgets all = new AllWidgets("blah", "foo", "bar")
  
  Console.Writeline("Widget A : " + all.wa);
  Console.Writeline("Widget B : " + all.wb);
  Console.Writeline("Widget C : " + all.wc);
}