div.sj-gridslider .gridslider-inner .item .item-wrap:after{
    position:absolute;
    opacity:0;
    transition: all 0.5s;
    -webkit-transition: all 0.5s;
}
div.sj-gridslider .gridslider-inner .item .item-wrap:after {
    content:'\A';
    width:100%; height:100%;
    top:0; left:0;
    background:rgba(0,0,0,0.7);
}
div.sj-gridslider .gridslider-inner .item .item-wrap:hover:after{
    opacity:1;
}