.container {
    display: flex;
    align-items: flex-start;
    justify-content: center;
    flex-wrap: wrap;
}

.card {
    flex: 1 1 1%;
    opacity: 0.5;
    position: relative;
    transition: flex 600ms cubic-bezier(0.25, 1, 0.5, 1), opacity 250ms ease;
    margin: 0.25rem;
}

.card:hover {
    flex-basis: 30%;
    opacity: 1;
}

.card__inner {
    background: #fff;
    border-radius: 8px;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden; 
    position: relative;
}

.card__inner picture {
    width: 100%;
    height: 0;
    padding-bottom: 600px;
    overflow: hidden;
    position: relative;
}

.card__inner picture img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
    object-position: center;
}

.card__caption {
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    padding: 0.6rem;
    background: rgba(0, 0, 0, 0.6);
    color: #fff;
    font-size: 0.9rem;
    text-align: center;
    opacity: 0;
    transition: opacity 0.5s ease;
    pointer-events: none;
    border-bottom-left-radius: 8px;
    border-bottom-right-radius: 8px;
}

.card:hover .card__caption {
    opacity: 1;
}

.container .card:nth-child(2),
.container .card:nth-child(5),
.container .card:nth-child(9),
.container .card:nth-child(13),
.container .card:nth-child(17) {
    margin-top: 0;
}

.container .card:nth-child(2),
.container .card:nth-child(4),
.container .card:nth-child(6),
.container .card:nth-child(8),
.container .card:nth-child(10),
.container .card:nth-child(12),
.container .card:nth-child(14),
.container .card:nth-child(16) {
    margin-top: 2.5%;
}

.container .card:nth-child(3),
.container .card:nth-child(7),
.container .card:nth-child(11),
.container .card:nth-child(15) {
    margin-top: 5%;
}