anchor.diff:  
   import 'dart:html';
   import 'dart:async';
  +import 'dart:math';
   import 'package:polymer/polymer.dart';
   
   @CustomTag('fold-button')
  
positive.code: 
      _restoreStyle(t.style, 'display');
  
      new Timer(DISPLAY_DELAY, () {
        _restoreStyle(t.style, 'transform', 'scale(1)');
        _restoreStyle(t.style, 'opacity', '1');
        startTransitionEndTimer();
      });
    }
  
    void startTransitionEndTimer() {
      if (_transitionEndTimer != null) {
        _transitionEndTimer.cancel();
      }
      _transitionEndTimer = new Timer(TRANSITION_DURATION, handleTransitionEnd);
    }
  
    void handleTransitionEnd() {
      final t = _targetElement;
      if (t == null) return;
  
  
negative.code:   }
  
    _setStyle(CssStyleDeclaration style, String propName, String value) =>
        _listWithVenderPrefix(propName).forEach((name) =>
            style.setProperty(name, value));
    _saveStyles(CssStyleDeclaration style) =>
        PROP_NAMES.forEach((p) => _saveStyle(style, p));
    _saveStyle(CssStyleDeclaration style, String propName) {
  