anchor.diff:  import "package:polymer/polymer.dart";
   import "dart:async";
   import "dart:html";
  +import "dart:math";
   
   import "deck/deck.dart";
   import "viewmodel/viewmodel.dart";
  
positive.code:       if (displacement == null)
          return;
        double distance = displacement.magnitude;
        double duration = distance / _kSettleVelocity;
        classes.add("moving");
        WebAnimations.animate(this, [{
          "transform": "translate(${-displacement.x}px, ${-displacement.y}px)"
  
negative.code:   bool isAttached = false;
  
    static const double _kSettleVelocity = 1.5; // dips per ms
    static const double _kMinSettleDuration = 200.0; // ms
    static const double _kMaxSettleDuration = 500.0; // ms
  
    FcCard.created() : super.created() {
    }
  