Hauptmenü

body {
  margin: 20px 2%;
  padding: 0px;
  background-color: #0080c0;
}
#links {
  float: left;
  width: 20%;
  height: 300px;
  background-color: #ffcc00;
}
#rechts {
  float: left;
  width: 20%;
  height: 300px;
  background-color: #ffcc00;
}
#inhalt {
  float: left;
  width: 52%;
  margin: 0px 2%;
  background-color: #ffffc6;
}
p.back {
  clear: both;
  text-align: center;
}

...

<div id="links">...</div>
<div id="inhalt">...</div>
<div id="rechts">...</div>
<p class="back">...</p>

Zweitmenü