anchor.diff:     * Creates the card with DOM given the [backImage] and [frontImage] and
      * appends it to [container].
      */
  -  factory Card.withDom(Node container, String backImage, String frontImage, id) {
  +  factory Card.withDom(Element container, String backImage, String frontImage, id) {
       var back = new ImageElement(src: backImage)
                   ..className = 'back';
       var front = new ImageElement(src: frontImage)
  
positive.code: 
  void main() {
    prepareGame();
  
  }
  
  void prepareGame() {
  
negative.code: 
      var div = new DivElement()
                  ..className = 'pexeso-card'
                  ..children.addAll([back, front]);
  
      container.children.add(div);
  
      return new Card(div, false, id);
    }
  