div#adv {
      background:#ccc;
      width:auto;
      margin:0;
      padding:0.5em;
}
div#main {
      float:right;
      width:75%;
      background:#0fc;
      margin-left:0.5em;
      padding:0.5em;
}
div#nav {
      background:#ddd;
      margin-right:75%;
      padding:0.5em;
}