MainPage = new NavigationPage(new MainPage())
    {
        BarBackgroundColor = Color.Blue,
        BarTextColor = Color.Yellow
    };

    Title = "Main Page";
    NavigationPage.SetBackButtonTitle(this, "Back");   //iOS only....

    Button gotoModelessButton = new Button
    {
        Text = "Go to Modeless Page",
        HorizontalOptions = LayoutOptions.Center,
        VerticalOptions = LayoutOptions.CenterAndExpand
    };

    gotoModelessButton.Clicked += async (sender, args) => { await Navigation.PushAsync(new ModelessPage()).ConfigureAwait(true); };