custom dialog Mahapps ShowMetroDialogAsync with close button

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C#

WPF

dialog

Metro-design

I create Mahapps custom dialog message with this code. the problem is the dialog form not show close button so cant close it. how to show close button ?

public async void button_Click(object sender, RoutedEventArgs e)    

  {      Button btn = (Button) sender;
        //dialog.Resources["CustomDialogTest"];
        string[] id =  btn.Name.ToString().Split('_');

        this.MetroDialogOptions.ColorScheme = MetroDialogColorScheme.Accented;
        var dialog = (BaseMetroDialog)this.Resources["CustomDialogTest"];

        var mySettings = new MetroDialogSettings()
        {
            AffirmativeButtonText = "OK",
            AnimateShow = true,
            NegativeButtonText = "Go away!",
            FirstAuxiliaryButtonText = "Cancel",               
        };
         await this.ShowMetroDialogAsync(dialog);
         // this for close the dialog -> await this.HideMetroDialogAsync(dialog);           
    }