.card-flex {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;   
}

/*
.card {
    min-width: 350px;   
}
*/
.card-flex .card {  
    margin-bottom: 5%;
    box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
}