html {
    font-size: 22px;
}

body {
    background-image: url("background.jpg");
    background-color: #333;
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    background-attachment: fixed;
    color: whitesmoke;
    min-height: 100vh;
}

header, main, section, nav {
    text-align: center;
}