Sizing the Stopwatch UI with AspectRatio


We will use a Stack to place all the (upcoming) UI elements within the same drawing area.

For now, this will contain the ElapsedTimeText widget, along with a square Container that we will use as a reference for learning about matrix transforms.

We don't want to set the width and height explicitly. Instead the layout engine should set the constraints that will determine the size of the stopwatch UI.

But we want to specify a fixed proportion between width and height. AspectRatio is great for that, and since we want a square, we can pass a value of 1.0:

  aspectRatio: 1.0,
  child: Stopwatch(),