body {
    background-color: skyblue;
}
@media only screen and (max-width: 646px) {
    .card{
        max-width: 100% !important;
        width: 100% !important;
        box-shadow: 2px 2px 4px rgba(0,0,0,0.2);
    }
    .card > img {
        height: auto !important;
    }
}