body{display:flex}nav{width:250px;overflow-y:auto;position:fixed;top:0;background:#ddd;bottom:0;}nav h2{margin-left:7px}nav ul{list-style:none;margin:0;padding:.5em}nav li{padding:0;padding-top:10px;margin:0;margin-bottom:5px;border-top:1px solid #bebebe}nav li:first-child{border:0}nav li li{padding-top:5px;margin:0;border:0}nav li li a{display:block;color:#444;padding:.25em .5em;text-decoration:none;}nav li li a:hover{background:#ccc}nav li li a.active{background:#444;color:#eee}iframe{margin-left:250px;border:0;flex:1}