#nav {
    display: inline-block;
    left: 0;
    right: 0;
    margin: 0 auto;
    padding: 0;
}

#nav ul,
#nav li {
    list-style: none;
    z-index: 999;
}

#nav ul {
    position: absolute;
    margin: 0px auto;
}

#nav li {
    width: 100px;
    vertical-align: middle;
    float: left;
    /* menu horizontal */
}

/* affichage sous menu au passage souris */
#nav li:hover>ul li {
    visibility: visible;
    position: relative;
    float: none;
}

/* sous menu */
#nav ul li {
    position: absolute;
    text-align: left;
    visibility: hidden;
    padding: 0px;
    margin: 0px 0px 0px -35px;
}

.menu-img {
    transition: all 300ms ease;
    border-radius: 5px;
    box-shadow: 5px 5px 5px rgba(255, 255, 255, 0.9);
}

.menu-img:hover {
    transition: all 300ms ease;
    box-shadow: 5px 5px 5px rgba(70, 130, 180, 0.9);
}

@media screen and (max-width:640px) {
    #nav li {
        width: 62px;
        margin: 0px 0px 0px 1px;
    }

    #nav ul li {
        margin: 0px 0px 0px -55%;
    }

    .menu-img {
        width: 63px;
    }
}