div#left_side_bar {
  float:left;
  width:21%;
  margin-left:-20.9%;
  padding: 0;
}
div#right_side_bar {
  float:right;
  width:21%; /* If the side column is the same width as the centre column then this percentage is 100% */
  margin-right:-20.9%; /* This is less than the width because this div must have some real existence in its parent div */
}
div#footer { 
  clear:both;
  border-top: none;
  background-color:#e5e7ec;
 }