body{
    color: white;
    
    margin: 0%;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    background-image: url('Bilder/laufen1.jpg');
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-size: cover;
}
/* Use a media query to add a breakpoint at 800px: */
@media screen and (max-width: 480px) 
{
    body{
        background-image: url('Bilder/Laufen4.jpg');
    }
}