* {
    margin: 0px;
    padding: 0px;
    font-family: Avenir, sans-serif;
}

nav {
    width: 100%;
    margin: 0 auto;
    background-color: lightgrey;
    position: sticky;
    top: 0px;
}

    nav ul {
        list-style-type: none;
    }

        nav ul li {
            float: left;
            width: 33%;
            text-align: center;
            position: relative;
        }

        nav ul::after {
            content: "";
            display: table;
            clear: both;
        }

    nav a {
        display: block;
        text-decoration: none;
        color: black;
        border-bottom: 2px solid transparent;
        padding: 10px 0px;
    }

        nav a:hover {
            color: orange;
            background-color: black;
            border-bottom: 2px solid gold;
        }

.sous {
    display: none;
    box-shadow: 0px 1px 2px #CCC;
    background-color: lightgrey;
    position: absolute;
    width: 100%;
    z-index: 1000;
}

nav > ul li:hover .sous {
    display: block;
}

.sous li {
    float: none;
    width: 100%;
    text-align: left;
}

.sous a {
    padding: 10px;
    border-bottom: none;
    text-align: center;
}

    .sous a:hover {
        border-bottom: none;
        background-color: RGBa(200,200,200,0.1);
        background-color: black;
    }

.deroulant > a::after {
    content: " ▼";
    font-size: 12px;
}

.conteneur {
    margin: 50px 20px;
    height: 1500px;
}