title: set background black with 50% opacity
body: <p>So, I have this div <code>#welcome</code> that runs this code</p>
  
  <pre><code>if ($.cookie('20120129') != '1') {
      $('#welcome').slideDown('slow');
      $.cookie('20120129', '1', { expires: 20 }); 
  }
  
  #welcome{
    position: absolute; z-index:100;
    background: #fff; color: #000;
    border: 1px solid black;
    display: none;
    width: 1000px;
    margin: 0 auto;
  }
  #welcome p{padding: 100px;}
  </code></pre>
  
  <p>I was wondering how to set a background layer between <code>#welcome</code> and the page with an 50% opicity, like thickbox/colorbox...</p>