Extend size of non client area using C#

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C#

GUI

I need to extend the size of the top edge of the client area to enter non GUI components that location. I am using the code below to this, however, by turning the extended area code is blank, you do not get the transparency of Windows 7 Professional, which is the OS I'm using.
I am new to programming and C # Windows API. I thank the attention.

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Runtime.InteropServices;
    using System.Windows.Forms;

    namespace InstrumentalCsharp
    {
    public partial class WExplorerPadrao : Form
    {

        [StructLayout(LayoutKind.Sequential)]
        public struct MARGINS
        {
            public int cxLeftWidth;      // width of left border that retains  its size
            public int cxRightWidth;     // width of right border that retains its size
            public int cyTopHeight;      // height of top border that retains its size
            public int cyBottomHeight;   // height of bottom border that retains its size
        };

    [DllImport("dwmapi.dll", PreserveSig = false)]
    public static extern void DwmExtendFrameIntoClientArea(IntPtr hwnd, ref     MARGINS margins);

    [DllImport("dwmapi.dll", PreserveSig = false)]
    public static extern bool DwmIsCompositionEnabled();


        public WExplorerPadrao()
        {
            InitializeComponent();
        }

    protected void WExplorerPadrao_Load(object sender, System.EventArgs e)
        {
            WExplorerPadrao.MARGINS margins = new WExplorerPadrao.MARGINS();
            margins.cxLeftWidth = 0;
            margins.cxRightWidth = 0;
            margins.cyTopHeight = 20;
            margins.cyBottomHeight = 0;
            IntPtr hwnd = this.Handle;
            WExplorerPadrao.DwmExtendFrameIntoClientArea(hwnd, ref margins);
        }
    }
}

What I have tried:

I tried extend the top of non client area in other languages, however, the result is the same as I described above.