#thumbnailContainer {
    display: flex;
    flex-wrap: wrap; /* allows wrapping into new rows */
    justify-content: flex-start; /* align items to left */
    align-items: flex-start; /* top align */
    gap: 0.75rem; /* space between thumbnails */
    padding: 1rem;
    overflow-y: auto; /* scrolls if too many rows */
    max-height: 60vh; /* keep room for close button */
}

    /* make sure thumbnails don’t stretch full width */
    #thumbnailContainer > * {
        flex: 0 0 auto; /* keeps them at natural size */
        display: inline-block; /* ensures side-by-side */
    }