body
 {
  background: #E2E2E2 url('images/background.jpg') top center repeat-x;
  margin: 0px;
 }

div#header_container
 {
  position: relative;
  margin-left: auto;
  margin-right: auto;
  z-index: 1;
  width: 800px;
  height: 100px;
  background: url('images/header_background.png') bottom center no-repeat;
 }