body {
    background-image: url("wallpaper.jpg");
    background-repeat: no-repeat;
    background-size: 100% 100vh;
}

#mail_link {
    width: 100px;
    height: 100px;
}

#mail {
    width: 100px;
    height: 100px;
    background-image: url("mail_icon.png");
    background-size: 100%;
}

a {
    display: block;
}