body {
    background: url(background.png);
}

@media screen and (max-width: 768px) {
a {
    text-decoration: none;
    font-weight: bold;
    font-size: 16px;
}
}

@media screen and (min-width: 768px) {
    li {
    display: inline;
    margin-right: 20px;
}
a {
    text-decoration: none;
    font-weight: bold;
    font-size: 16px;
}

}
header ul {
    list-style: none;
    padding: 0;
}