.ad-320x300 {
    width: 320px;
    max-width: 100%;
    margin: 20px auto;
    text-align: center;
    box-sizing: border-box;
}

.ad-320x300 img {
    display: block;
    width: 320px;
    max-width: 100%;
    height: 300px;
    object-fit: contain;
    margin: 0 auto;
}

@media (max-width: 340px) {
    .ad-320x300 {
        width: 100%;
    }

    .ad-320x300 img {
        width: 100%;
        height: auto;
        aspect-ratio: 320 / 300;
    }
}