title: Absolute positioned div needs bottom margin on document with fixed footer
body: <p>Somehow I can't figure out what I'm missing...</p>
  
  <p>I try to position a number of <code>absolute</code> divs between two <code>fixed</code> bars (header and footer). Header contains some tabs and footer contains an copyright. I want to use the window's scrollbar and not an overflowed div and I know it should be possible! </p>
  
  <p>Every absolute positioned div should carry an extra margin, so that the bottom of that div does not disappear behind the footer.</p>
  
  <p><img src="https://i.stack.imgur.com/Fdf4l.png" alt="enter image description here"></p>
  
  <p>It should become something like this:
  <img src="https://i.stack.imgur.com/ChKbU.png" alt="enter image description here"></p>
  
  <p>A snippet of my problem is available <a href="http://jsfiddle.net/LnEv2/" rel="noreferrer">here</a> on jsfiddle.</p>
  
  <p>My HTML:</p>
  
  <pre><code>&lt;ul class="cf tabs"&gt;
      &lt;li&gt;Tab 1&lt;/li&gt;
      &lt;li&gt;Tab 2&lt;/li&gt;
  &lt;/ul&gt;
  &lt;div style="margin-top: 40px; padding-bottom: 30px; position:relative"&gt;
      &lt;div style="position:absolute;top:300px; height:100px; width: 250px; left:200px; border: 1px solid purple;"&gt;aaa&lt;/div&gt;
  
      &lt;div style="position:absolute;top:0px; height:100px; width: 100px; left:100px; border: 1px solid purple;"&gt;bbb&lt;/div&gt;
  
      &lt;div style="position:absolute;top:450px; height:100px; width: 250px; left:400px; border: 1px solid purple;"&gt;ccc&lt;/div&gt;
  &lt;/div&gt;
  &lt;div class="cf footer"&gt;Copyright &amp;copy;&lt;/div&gt;​
  </code></pre>
  
  <p>The stylesheet I'm using:</p>
  
  <pre><code>    ul.tabs {
          list-style-type: none;
          list-style-position: outside;
          padding:5px;
          margin: 0;
          position:fixed;
          top:0;
          z-index: 999;
          background-color: white;
          left:0;
          right:0;
          border-bottom: 1px solid green;
          opacity: 0.7;
      }
      ul.tabs li {
          float: left;
          margin:1px;
          padding: 4px 10px 2px 10px;
          border: 1px solid black;
      }
  
  
      div.footer {
          position: fixed;
          bottom: 0;
          left: 0;
          right:0;
          background-color:#DEDEE9;
          border-top: 3px outset #BBBBBB;
          padding: 5px;
          opacity: 0.6;
      }
  
      .cf:before,
      .cf:after {
          content: " "; 
          display: table; 
      }
      .cf:after {
          clear: both;
      }​
  </code></pre>
  
  <p>Do you guys have any hints?</p>
  
  <p><strong>Extra info</strong>
  As you can see in the attached image the purple border of squared div at bottom right is overlapping the fixed footer. I do not want this. There should be given a bottom margin somewhere, so that every div carries an extra margin so it should match the top of the footer</p>