header {
    color: white;
    text-align: center;
    background-color: black;
    background-size: cover;
 }
 nav {
    background-color: green;
    float: left;
    width: 10%;
    clear: left;
    min-height: 650px;
    border-right: 1px solid black;
 }
.menu {
    width: 15%;
}

.menu li {
 margin-left: -2.5em;
 background-color: red; 
}

.menu a { 
    color: white; 
    display: block;
    padding: 10px;
    text-decoration: none;
}

.menu a:hover {
    background-color: #c0c0c0;
}

 section {
    float: left;
    width: 80%;
    padding-left: 1em;
    background-color: aliceblue;
 }
 
 footer {
    clear: both;
    text-align: center;
    background-color: white;
 }