body {
  margin: 20px;
  text-align: center;  /* nur für alte Browser */
  background-color: #0080c0;
}
#box {
  width: 400px;
  margin: 0px auto;
  padding: 15px;
  text-align: left;
  background-color: #ffffc6;
}

...

<div id="box">...</div>