title: How to make a footer div always on the bottom of a page
body: <p>When a popup windows opened and enlarged the body's height</p>
  
  <p>the footer should go to the bottom of page,but I cannot find how to do that</p>
  
  <p>here is my code</p>
  
  <pre><code>&lt;style&gt;
  .div1{
  width:360px;
  height:240px;
  overflow:auto;
  overflow-x:hidden;
  border:1px solid #f00;
  position:absolute;
  }
  .black_overlay{ 
  display: none; 
  position: fixed; top: 0%; left: 0%; width: 100%; height: 100%;
  background-color: black; z-index:1001; -moz-opacity: 0.8; opacity:.80; filter: alpha(opacity=80); }
  .white_content { 
  display: none; 
  position: absolute; 
  top: 25%; left: 25%; width: 50%;
  padding: 16px; border: 16px solid orange; background-color: white; z-index:1002; overflow: auto; }
  &lt;/style&gt; 
  &lt;a onclick="document.getElementById
  ('light').style.display='block';document.getElementById('fade').style.display='block'" href="javascript:void(0)"&gt;open&lt;/a&gt;  
  
  &lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;
  &lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;
  
  &lt;div class="div1"&gt;
  footer&lt;/div&gt;
  &lt;div id="light" class="white_content"&gt;content
  &lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;
  &lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;
  &lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;
  &lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;&lt;br&gt;
  &lt;a onclick="document.getElementById
  ('light').style.display='none';document.getElementById('fade').style.display='none'" href="javascript:void(0)"&gt;close&lt;/a&gt;
  &lt;/div&gt; 
  &lt;div id="fade" class="black_overlay"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>Thanks for reading this</p>
  
  <p>Any suggestion will be appreciated.</p>