anchor.diff:              child: new _IgnorePointerWhileStatusIsNot(
                 AnimationStatus.completed,
                 controller: _controller,
  -              child: widget.frontLayer,
  +              child: new FadeTransition(
  +                opacity: _frontOpacity,
  +                child: widget.frontLayer,
  +              ),
               ),
             ),
           ),
  
positive.code: class _BackdropState extends State<Backdrop> with SingleTickerProviderStateMixin {
    final GlobalKey _backdropKey = new GlobalKey(debugLabel: 'Backdrop');
    AnimationController _controller;
  
    @override
    void initState() {
  
negative.code:       value: 1.0,
        vsync: this,
      );
  
      _frontOpacity =
        new Tween<double>(begin: 0.2, end: 1.0).animate(
          new CurvedAnimation(
            parent: _controller,
            curve: const Interval(0.0, 0.4, curve: Curves.easeInOut),
          ),
        );
    }
  
    @override
  