title: Change background colour of ul li
body: <p>I struggle with the problem, that I want to change the background colour of my ul item, when the li is clicked.
  So, I open a dropdown menu, click on the li link, and now I want that the mainmenuslot changes its backgroundcolor.</p>
  
  <p>I am working with this code:</p>
  
  <pre><code>#mainnav-menu ul li.current_page_item a, #mainnav-menu ul li.current-menu-item a {
      background-color: #004494;
      background: #004494;
      text-decoration: none;
      color: #ffffff;
      font-weight: bold;
  }
  </code></pre>
  
  <p>What do I have to add, to get this function? I tried it with #mainnav-menu ul a, #mainnav-menu ul, and a lot of other possibilities.</p>