.gallery ul {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(2, 1fr);
    grid-column-gap: 3px;
    grid-row-gap: 0px;
}
    .gallery ul .long img {
        max-height: 72vh;
    }

@media screen and (width <= 600px) {
    .gallery ul {
        display: grid;
        grid-template-columns: 1fr;
        grid-template-rows: repeat(3, 1fr);
        grid-column-gap: 0px;
        grid-row-gap: 0px;
    }
}