a[data-fslightbox] {
    position: relative;
}

a[data-fslightbox]::after {
    content: '';
    position: absolute;
    bottom: 1rem;
    right: 1rem;
    width: 48px;
    height: 48px;
    background-color: #ccc;
    background-image: url(../img/zoom-in.svg);
    background-repeat: no-repeat;
    background-position: center;
    opacity: 0;
    transition: opacity .3s;
    z-index: 3;
    border-radius: 50%;
}

a[data-fslightbox]:hover::after {
    opacity: 1;
}