body {
    margin:0px;
    font-family: arial;
}
#kopf {
    background-image: url("Bilder/dji_0031.jpg");
    background-position: center;
    background-size: cover;
    background-repeat:"no-repeat";
    height:400px;
}
#kopf a {
    color:black;
    text-decoration: none;
    font-size: 200%;
    font-weight: bold;
    margin-top: 15pt;
    margin-left: 25px;
}
#nav a:hover {
    background-color: lightgrey;
    border-top:solid 5px red;
}
#nav a {
    width: 25%;
    display: inline-block;
    float: left;
    text-align: center;
    text-decoration: none;
    color:black;
}
#nav1 {
    border-top:solid 5px lightgreen;   
}
#nav2 {
    border-top:solid 5px orange;   
}
#nav3 {
    border-top:solid 5px lightblue;   
}
#nav4 {
    border-top:solid 5px violet;   
}