anchor.diff:  import 'package:sky/widgets/widget.dart';
   import 'package:vector_math/vector_math.dart';
   
  -const Duration _kCardDismissFadeout = const Duration(milliseconds: 300);
  +const Duration _kCardDismissFadeout = const Duration(milliseconds: 200);
   const double _kMinFlingVelocity = 700.0;
   const double _kMinFlingVelocityDelta = 400.0;
   const double _kFlingVelocityScale = 1.0/300.0;
  
positive.code:       if (_performance.isCompleted)
          _maybeCallOnDismissed();
        else if (!_performance.isAnimating)
          _performance.progress = 0.0;
      });
    }
  
  
negative.code:   }
  
    void _maybeCallOnDismissed() {
      _performance.stop();
      _performance.removeListener(_handleAnimationProgressChanged);
      if (onDismissed != null)
        onDismissed();
    }
  