body {
    background-color: aliceblue;
    margin-left: auto;
    margin-right: auto;
}
nav{position:fixed;}
footer {
    color: white;
    background-color: black;
    bottom: 0px;
    text-align: center;
    position: fixed;
    width: 100%;
}
footer a {
    text-decoration: none;
    color: white;
}

footer a:hover {
    text-decoration: none;
    color: red;
}
h1 {
    color: black;
}

span,
li a {
    color: red !important;
}

.box {
    background-color: transparent;
    width: 220px;
    height: 300px;
    perspective: 1000px;
    margin-bottom: 35px;
}

.box-inner {
    position: relative;
    width: 100%;
    height: 100%;
    text-align: center;
    transition: transform 0.8s;
    transform-style: preserve-3d;
}

.box:hover .box-inner {
    transform: rotateY(180deg);
}

.box-front,
.box-back {
    -webkit-backface-visibility:hidden;
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 20px;
    box-shadow: 20px;
}

.box-front {
    background-color: #cccccc;
    color: #111111;
}

.box-back {
    padding: 10px;
    background-color: #dfa908;
    color: black;
    transform: rotateY(180deg);
}

img {
    width: 150px
}

#myBtn {
    display: none;
    position: fixed;
    bottom: 30px;
    right: 15px;
    z-index: 99;
    font-size: 18px;
    border: none;
    outline: none;
    background-color: red !important;
    color: white;
    cursor: pointer;
    padding: 15px;
    border-radius: 4px;
}

#myBtn:hover {
    background-color: green !important;
}

@media screen and (max-width:767px) {

    .box {
        margin-bottom: 20px;
    }
}

.haut-droite{
    z-index: 10000;       /* pour mettre au dessus des autres */
    position: absolute;      /* la fameuse position fixed */ 
    top: 1px;            /* décalage des bords */
    right: 1em;
    padding: .5em;        /* donne de l'air au texte */
}
.dropdown button{
    color: red !important;
    border: none;
}