body {
    background-repeat: no-repeat;
    background-position: 50% 50%;
    background-attachment: fixed;
    background-size: cover;
}
h1 {
    font-size: 50px;
    text-align: center;
}
#lwhderwoche {
    text-align: center;
    margin: auto;
    opacity: 0.7;
    background-color: beige;
    width: 80%;
    font-size:30px;
}
#zurueckbutton {
    background-color: grey;
    width: 60px;
    height: 60px;
    border-radius: 40px;
    position: absolute;
}