AnimatedWidget Return a SlideTransition
with the Animation<Offset> and the child widget:

4. Use a CurveTween

Flutter provides a selection of easing curves that
adjust the rate of the animation over time.
The Curves class
provides a predefined set of commonly used curves.
For example, Curves.easeOut
makes the animation start quickly and end slowly.

To use a Curve, create a new CurveTween
and pass it a Curve:

This new Tween still produces values from 0 to 1. In the next step, it will be
combined the Tween<Offset> from step 2.

5. Combine the two Tweens

To combine the tweens,
use chain():

Then use this tween by passing it to animation.drive(). This creates a new
Animation<Offset> that can be given to the SlideTransition widget: