How do I change the size of a window?

Question

I start with an initial content page with a size of 1285 x 800. I'm using shell navigation and I say Shell.Current.Navigation.PushModalAsync(new NewDb()); and in the NewDb content page I have:

protected override void OnAppearing()
{
    base.OnAppearing();

    Window.Height =  450;
}

In a button of the NewDb page I have Shell.Current.Navigation.PopAsync(); but when I return back to the first page, it remains the height of 450. How do I resize the height to 800?

I tried entering code in the OnAppearing() code-behind in the first page but that doesn't seem to work.