C#: 付箋紙みたいにどこを掴んでも移動できるようにするには

class StickyNote{
static void Main(){
Application.Run(new MainWindow());
}
}

class MainWindow : Form{
private Label label;
private Point mousePoint; //マウスのクリック位置を記憶

public MainWindow(){
this.Width = 200;
this.Height = 100;
this.FormBorderStyle = FormBorderStyle.None;
this.ShowInTaskbar = false;

//フォームに目いっぱいLabelを貼っておく。Labelをダブルクリックしたら終了
label = new Label(){
Dock = DockStyle.Fill,
BackColor = Color.LightPink,
BorderStyle = BorderStyle.FixedSingle,
Parent=this,
};
label.DoubleClick += new EventHandler(DoubleClicked);
label.MouseDown += new MouseEventHandler(MouseDowned);
label.MouseMove += new MouseEventHandler(MouseMoved);

}

//フォームダブルクリック時終了
private void DoubleClicked(object sender, EventArgs e){
Application.Exit();
}

//マウスのボタンが押されたとき
private void MouseDowned(object sender, System.Windows.Forms.MouseEventArgs e){
if ((e.Button & MouseButtons.Left) == MouseButtons.Left){
mousePoint = new Point(e.X, e.Y); //位置を記憶する
}
}

//マウスが動いたとき
private void MouseMoved(object sender, System.Windows.Forms.MouseEventArgs e){
if ((e.Button & MouseButtons.Left) == MouseButtons.Left){
this.Location = new Point(
this.Location.X + e.X – mousePoint.X,
this.Location.Y + e.Y – mousePoint.Y);
}
}
}