title: -webkit-transform: incremental reposition with += operator not working
body: <p>I am trying to incrementally reposition an element by setting the <code>-webkit-transform</code> property to <code>+=200px</code></p>
  
  <p>But it doesn't work. I'm missing something, but don't know what.</p>
  
  <ul>
  <li><strong><a href="http://jsfiddle.net/yVSDC/" rel="nofollow">http://jsfiddle.net/yVSDC/</a></strong></li>
  </ul>
  
  <p>Clicking the div is supposed to move it further down by 200px everytime.</p>