title: css/ jQuery - center absolute positioned div
body: <p>The div is 50% opaque and is displayed on top of the site's content, and it has a fixed width of 960 pixels (it's created by jQuery).</p>
  
  <p>How can I center it horizontally?</p>
  
  <p><code>margin: 0 auto;</code> doesn't work :(</p>