body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background: #f4f4f4;
}
header {
    background: #333;
    color: #fff;
    padding: 1em;
    text-align: center;
}
nav a {
    margin: 0 15px;
    color: #fff;
    text-decoration: none;
}
main {
    padding: 2em;
}
footer {
    background: #333;
    color: #fff;
    text-align: center;
    padding: 1em;
    position: fixed;
    bottom: 0;
    width: 100%;
}
@media (max-width: 600px) {
    nav a {
        display: block;
        margin: 10px 0;
    }
}