Stack({Key key, FractionalOffset alignment: FractionalOffset.topLeft, Overflow overflow: Overflow.clip, List<Widget> children: const [] })

Creates a stack layout widget.

By default, the non-positioned children of the stack are aligned by their top left corners.

Source 

Stack({
  Key key,
  this.alignment: FractionalOffset.topLeft,
  this.overflow: Overflow.clip,
  List<Widget> children: const <Widget>[],
}) : super(key: key, children: children);