Visual Studio C#
.net Framework

Hi, I have followed this tutorial: https://www.youtube.com/watch?v=oKQlPE57gYg to 4:20 but after testing then I got this error message and I don’t know how to fix it.

Error Message

This is all my code

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

namespace Energy_Organizer
{
    public partial class Form1 : Form
    {
        private bool drag;
        private int mouseX;
        private int mouseY;

        private const int WM_NCHITTEST = 0x84;
        private const int HTCLIENT = 0x1;
        private const int HTCAPTION = 0x2;

        private bool m_aeroEnabled;

        private const int CS_DROPSHADOW = 0x00020000;
        private const int WM_NCPAINT = 0x0085;
        private const int WM_ACTIVEAPP = 0x001C;

        [System.Runtime.InteropServices.DllImport("dwmapi.dll")]

        public static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);
        [System.Runtime.InteropServices.DllImport("dwmapi.dll")]

        public static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int attrValue, int attrSize);
        [System.Runtime.InteropServices.DllImport("dwampi.dll")]

        public static extern int DwmIsCompoisionEnabled(ref int pfEnabled);
        [System.Runtime.InteropServices.DllImport("Gdi32.dll", EntryPoint = "CreateRoundRectRgn")]
         private static extern IntPtr CreateRoundRectRgn
            (
            int nLeftRect,
            int nTopRect,
            int nRightRect,
            int nBottomRect,
            int nWidthEllipse,
            int nHeightEllipse
            );

        public struct MARGINS
        {
            public int leftWidth;
            public int rightWidth;
            public int topHeight;
            public int bottomHeight;
        }

        protected override CreateParams CreateParams
        {
            get
            {
                m_aeroEnabled = CheckAeroEnabled();
                CreateParams cp = base.CreateParams;
                if (!m_aeroEnabled)
                    cp.ClassStyle |= CS_DROPSHADOW; return cp;
            }
        }

        private bool CheckAeroEnabled()
        {
            if (Environment.OSVersion.Version.Major >= 6)
            {
                int enabled = 0; DwmIsCompoisionEnabled(ref enabled);
                return (enabled == 1) ? true : false;
            }
            return false;
        }

        protected override void WndProc(ref Message m)
        {
            switch (m.Msg)
            {
                case WM_NCPAINT:
                    if (m_aeroEnabled)
                    {
                        var v = 2;
                        DwmSetWindowAttribute(this.Handle, 2, ref v, 4);
                        MARGINS margins = new MARGINS()
                        {
                            bottomHeight = 1,
                            leftWidth = 0,
                            rightWidth = 0,
                            topHeight = 0
                        }; DwmExtendFrameIntoClientArea(this.Handle, ref margins);
                    }
                    break;
                default: break;
            }
            base.WndProc(ref m);
            if (m.Msg == WM_NCHITTEST && (int)m.Result == HTCLIENT) m.Result = (IntPtr)HTCAPTION;
        }

        public Form1()
        {
            InitializeComponent();
        }
    }
}

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Controls;
using System.Windows.Forms;

namespace Energy_Organizer
{
    internal class Gradient_Sidebar_Panel : System.Windows.Forms.Panel
    {
        public Color gradientTop {get; set;}
        public Color gradientBottom {get; set;}

        protected override void OnPaint(PaintEventArgs e)
        {
            LinearGradientBrush linear = new LinearGradientBrush(this.ClientRectangle, this.gradientTop, this.gradientBottom, 90F);
            Graphics graphics = e.Graphics;

            graphics.FillRectangle(linear, this.ClientRectangle);
            base.OnPaint(e);
        }
    }
}

I have already tried the basic tipps from Visual Studio but nothing works.
I hope somebody can Help me 🙂 Thx