body {
    margin: auto;
    background: black;
}
main {
    width: 800px;
    margin:auto;
    margin-top: 20px;
    margin-bottom: 20px;
    text-align: center;
    background: white;
    padding: inherit;
    border: 10px;
    border-color: black;
    padding-bottom: 20px;
    padding: 10px;
}
header {
    width: 720px;
    margin: auto;
    background-image: url(bild42.jpg);
    height: 100px;
    color: white;
    padding: 50px;
    text-align: center;
    background-size: auto;
    font-family: sans-serif;
    border-top-color: black;
}
nav {
    border: 10px;
    border-color: black;
    text-align: center;
    background: white;
    width: 800px;
    margin: auto;
    height: 50px;  
    color: skyblue;
    padding: 10px;
}
.active {
    color: black;
}