#nav {
 width: 100%;
 background: red;
 min-height: 100px;
 }
 
#navleft {
 float: left;
 width: 60%;
 min-height: 100px;
 background: green;
 }
 
#navright {
 float: right;
 min-height: 100px;
 width: 40%;
 background: blue;
}