title: Vaadin MenuItem.setStyleName won't work
body: <p>I try to change the color of the items after this one is selected in vaadin. but no menuItems is selected when I click of an items.</p>
  
  <pre><code>   MenuBar.MenuItem previous = null;
  
      void createMenuBar(){
  
          menuBar = new MenuBar();
          menuBar.addItem("First Item", menuItem -&gt; {
              if (previous != null)
                  previous.setStyleName(null);
                  menuItem.setStyleName("selected");
                  previous = menuItem;
                  someActions();
          });
          menuBar.addItem("Second Item", menuItem -&gt; {
              // same action 
      });
  </code></pre>
  
  <p>Here a part of my style.css</p>
  
  <pre><code>.v-menubar-user-menu .v-menubar-menuitem-selected {
      color: #e2f6e7;
      text-shadow: 0 -1px 0 rgba(0, 0, 0, 0.05);
  }
  
  .v-menubar-user-menu .v-menubar-menuitem-selected:hover {
      color: #e2f6e7;
  }
  </code></pre>