nav {
    float: left;
    max-width: 400px;
    margin: 0;
    padding: 1em;
}

article {
    margin-left: 410px;
    border-left: 1px solid gray;
    padding: 1em;
}

header {
    color: white;
    background-color: black;
    clear: left;
    text-align: center;
}

footer {
    color: white;
    background-color: grey;
    clear: left;
}
