Show me how I can use Xamarin Forms to open a custom popup with Xamarin Forms Shell?

I would like to have a simple XF Andoid / iOS Shell project that demonstrates the same functionality as this: await [login to view URL]("Title", "Message", "Ok"); But using a custom XAML page instead of DisplayAlert Note that it must be a Shell application with a couple of screens, a button on one screen to open the popup and a button on the popup to close it. If you have already done this before it should be a very easy project. The deliverable will be a simple working XF app that I can download.