body {
    margin: 0;
    padding: 0;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 19px;
}
nav {
    background-color: #f3f3f3;
    border-bottom: 1px solid black;
    text-align: right;
    padding: 20px;
}
.menu {
    list-style: none;
    padding: 0;
    margin: 0;
}
.menu li {
    display: inline;
    margin: 15px;
}
.menu a {
    color: black;
    text-decoration: none;
}
.voir-menu, .cacher-menu {
    display: none;
}
@media screen and (max-width: 900px) {
    .voir-menu, .cacher-menu {
        display: block;
        font-size: 30px;
        cursor: pointer;
        transition: 0.5s;
    }
    .voir-menu:hover, .cacher-menu:hover {
        color: #777;
        transition: 0.5s;
    }
}