aspect ratio css

style.css

.post {
    width:320px;
    position: relative;
    background-color: #dbdbdb;
}

.post::after {
    display: block;
    content: "";
    /* 1:1 */
    padding-bottom: 100%;
    /* 16:9 = 56.25% */
}

.post img {
    width: 100%;
    height: 100%;
    vertical-align: top;
    object-fit: cover;
    position: absolute;
    left: 0;
    top: 0;
}