#overview {
    background: linear-gradient(to bottom, darkmagenta, darkslateblue);
}

#description {
    background: linear-gradient(to bottom, rosybrown, sienna);
}

#diagrams {
    background: linear-gradient(to bottom, darkgoldenrod, goldenrod);
}

#videos {
    background: linear-gradient(to bottom, darkblue, slateblue);
}