div.container {
    width: 100%;
    max-width: 21cm;
}
header {
    width: 100%;
}
/* navigation menu */
nav.left {
    float: left;
    max-width: 160px;
}
nav.right {
    float: right;
    max-width: 160px;
}
nav.top {
    display: inline-block;
    width: 100%;
}
article {
    padding: 1em;
}
footer {
    margin-top: 2em;
}