title: CSS addClass doesn't change background-image
body: <p>I want to apply image "bars_small.png" (which is the white image that you see on hover) when I make this button active.  </p>
  
  <p>The jQuery:  </p>
  
  <pre><code>        $("#btn_bars").click(function(){
              if(!$(this).hasClass('btn_header_active')){
                      $('.ch-grid .btn_header_active').removeClass('.btn_header_active');
                      $(this).addClass('btn_header_active');
                  });
              }
          });
  </code></pre>
  
  <p>CSS: </p>
  
  <pre><code>#btn_bars .btn_header_active .ch-info{
  
      background-image: url(http://www.zwoop.be/develop/images/fisheye/bars_small.png);
      background-repeat: no-repeat;
      background-position: center;
  }
  </code></pre>
  
  <p>I refer to this jsFiddle for the complete menu code and the visual effect: 
  <a href="http://jsfiddle.net/kimgysen/6ryav/" rel="nofollow">http://jsfiddle.net/kimgysen/6ryav/</a></p>