title: CSS3 calc() doesn't work with position fixed/absolute
body: <p>Does anyone know a workaround for this?</p>
  
  <p>I'm trying to calculate width of a div :</p>
  
  <pre><code>#container {
      position: fixed;
      top: 0;
      left: 0;
      z-index: 9;
      display: none;
      background: #fff;
      width: calc(100% - 1em);
      padding: .5em;
  }    
  </code></pre>