#contenedor{
    width: 900px;
    height: auto;
    margin: 0 auto;
    perspective: 1200;
    -webkit-perspective:1200;
    overflow:hidden;
}

.carta {
    width: 250px;
    height: 250px;
    position: relative;
    -webkit-transform-style: preserve-3d;
    transform-style: preserve-3d;
    -webkit-transition: all 1s;
    transition: all 1s;
    display:inline-block;
    margin: 20px;
}
.carta:hover{
    -webkit- transform: rotateY(180deg);
    transform: rotateY(180deg);
}
.lado {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    -webkit-backface-visibility: hidden;
    backface-visibility: hidden;
}

#frente {
    background-color: skyblue;
}

#atras {
    
    background-color: beige;
    -webkit- transform: rotateY(180deg);
    transform: rotateY(180deg);
}