Скачать или смотреть Flutter AnimatedContainer

In this video you learn how to animated the properties of container.
Some tips in video:
#setState() method : Notify the framework that the internal state of this object has changed. Whenever you change the internal state of a State object, make the change in a function that you pass to setState.
#StatefulWidget class : A widget that has mutable state.State is information that (1) can be read synchronously when the widget is built and (2) might change during the lifetime of the widget. It is the responsibility of the widget implementer to ensure that the State is promptly notified when such state changes, using State.setState.