Flex constructor
      
      Flex({ 
    
    
- required Axis direction,
 - MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
 - MainAxisSize mainAxisSize = MainAxisSize.max,
 - CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,
 - VerticalDirection verticalDirection = VerticalDirection.down,
 - List<
Widget> children = const <Widget>[], 
Implementation
Flex({
  required this.direction,
  this.mainAxisAlignment = MainAxisAlignment.start,
  this.mainAxisSize = MainAxisSize.max,
  this.crossAxisAlignment = CrossAxisAlignment.center,
  this.verticalDirection = VerticalDirection.down,
  List<Widget> children = const <Widget>[],
}) : super(children: children);