anchor.diff:  
     void removeChild(VNode container, VNode node) {
       final e = (node.ref as html.Element);
  +    final transitionNode = _nodes[node.key];
  +
  +    if (transitionNode.state == _CssTransitionNode.enter) {
  +      e.classes.remove('enter');
  +      e.classes.remove('active');
  +    }
  +    transitionNode.state = _CssTransitionNode.leave;
  +
       e.classes.add('leave');
       scheduler.currentFrame.read().then((_) {
         e.getComputedStyle().transform;
  
positive.code: 
  library uix.src.misc.css_transition_container;
  
  import 'dart:html' as html;
  import '../env.dart';
  import '../container.dart';
  import '../vcontext.dart';
  import '../vnode.dart';
  
  /// *EXPERIMENTAL* class for group transitions
  /// (doesn't work properly, proof of concept)
  abstract class CssTransitionContainer implements Container {
    html.Element get element;
  
    void initTransitionListeners() {
      element.onTransitionEnd.listen(_handleTransitionEnd);
  
negative.code:   void _handleTransitionEnd(html.TransitionEvent e) {
      e.stopPropagation();
  
      final html.Element target = e.target;
      final key = _nodeKeys[target];
      if (key != null) {
        final transitionNode = _nodes[key];
        switch (transitionNode.state) {
          case _CssTransitionNode.normal:
            break;
          case _CssTransitionNode.enter:
            final classes = target.classes;
            classes.remove('enter');
            classes.remove('active');
            transitionNode.state = _CssTransitionNode.normal;
            break;
          case _CssTransitionNode.leave:
            target.remove();
            transitionNode.node.dispose();
            _nodes.remove(key);
            _nodeKeys.remove(target);
            break;
        }
      }
    }
  
    void insertChild(VNode container, VNode node, VNode next) {
      assert(invariant((node.flags & VNode.componentFlag) != 0,
             'CssTransitionContainer can control Component nodes only.'));
      assert(invariant((node.key != null),
             'CssTransitionContainer can control nodes with explicit keys only.'));
  
      final nextRef = next == null ? null : next.ref;
      node.create((this as VContext));
  