.card-mod {
    display: inline-block;
    float: none;
    margin: 5px;
    position: relative;
    height: 340px;
    min-width: 220px;
    overflow-y: auto;
}

.card .overlay {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    max-height: 100%;
    max-width: 100%;
    opacity: 0;
    transition: .5s ease;
    background-color: #343a40c5;
    font-size: 1rem;
    color: white;
}

.card img {
    max-height: 100%;
    height: 100%;
}
  
.card:hover .overlay {
    opacity: 1;
}