#overview {
    background: linear-gradient(to bottom, brown, darkgoldenrod);
}

#description {
    background: linear-gradient(to bottom, seagreen, mediumseagreen);
}

#diagrams {
    background: linear-gradient(to bottom, grey, lightblue);
}

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