div.lightbox-container{
    position: relative;
}
    div.lightbox-container img.overlay-img {
        position: absolute;
        visibility: hidden;
        z-index: 10000;
    }
    div.lightbox-container:hover img.overlay-img {
        visibility: visible;
    }
    div.lightbox-container:hover img.lightbox {
        filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale"); /* Firefox 10+, Firefox on Android */
        filter: gray; /* IE6-9 */
        -webkit-filter: grayscale(100%);
    }