body {
    background-image: url(background.svg);
    background-size: cover;
    background-attachment: fixed;
}
.conteneurImage {
    text-align: center;
}
.grandeImage {
    width: 40%;
}
#imagePileCailloux {
    padding: 0 5% 0% 0;
}
.petiteImage {
    width: 10em;
    transition: width 1s;
}
.petiteImage:hover {
    width: 15em;
    transition: width 1s;
}