nested navigation demo
Created an app named colorimeter using flutter which is a nested navigation app with multiple navigators at bottom navigation bar. App has three menu buttons at bottom which consists of Red button, Green button and Blue button. Each individual screen consists of colour range from 50 to 900 and one open it also to view it in larger perspective.

Shorter version:
Created an app with a Scaffold and a BottomNavigationBar.
In the Scaffold body, created a Stack with one child for each tab.
Each child is an Offstage widget with a child Navigator.
Handled Android back navigation with WillPopScope.