Practical solution to center vertically and horizontally in HTML that works in FF, IE6 and IE7

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
 <title>Centering</title>
 <style type="text/css" media="screen">
  body, html {height: 100%; padding: 0px; margin: 0px;}
  #outer {width: 100%; height: 100%; overflow: visible; padding: 0px; margin: 0px;}
  #middle {vertical-align: middle}
  #centered {width: 280px; margin-left: auto; margin-right: auto; text-align:center;}
 </style>
</head>
<body>
 <table id="outer" cellpadding="0" cellspacing="0">
  <tr><td id="middle">
   <div id="centered" style="border: 1px solid green;">
    Centered content
   </div>
  </td></tr>
 </table>
</body>
</html>

#horizon
    {
    text-align: center;
    position: absolute;
    top: 50%;
    left: 0px;
    width: 100%;
    height: 1px;
    overflow: visible;
    display: block
    }

#content
    {
    width: 250px;
    height: 70px;
    margin-left: -125px;
    position: absolute;
    top: -35px;
    left: 50%;
    visibility: visible
    }

<div id="horizon">
   <div id="content">
      <p>This text is<br><emphasis>DEAD CENTRE</emphasis ><br>and stays there!</p>
   </div><!-- closes content-->
</div><!-- closes horizon-->

<style>
body
{
    text-align:left;
}
.MainBlockElement
{
    text-align:center;
    margin: 0 auto;
}
</style>