header {
    background-color:3F5773;
    color:white;
    clear:both;
    text-align:center;
    padding:5px; 
}
nav {
    line-height:30px;
    background-color:#eeeeee;
    height:600px;
    width:100px;
    float:left;
    padding:5px; 
}

footer {
    background-color:#3F5773;
    color:white;
    clear:both;
    text-align:center;
    padding:5px; 
}

a:hover {
  color: blue ;
  background-color: #def ;
}