body{ position: relative; } body,html{ width: 100%; height: 100%; } header{ height: 100px; width: 100%; background-color: #f00; } nav{ position: absolute; width: 100px; height: 100%; background-color: #000; left: 0; top:0; padding-top: 100px; } section{ width: 100%; height: 100%; padding-left: 100px; }