.gallery-box {
    position: relative;
    padding-bottom: 65%;
    overflow: hidden;
    height: 0;
    float:  left;
    width:  100%;
    border: 1px solid #fff;
}


.portfolio-box-caption {
    position: absolute;
    padding: 10px;
    background: rgba(0,0,0,0.5);
    height: 100%;
    width: 100%;
    color: #fff;
    top: 0;
    transition: all 1s;
    opacity: 0
}



.portfolio-box:hover .portfolio-box-caption {
    opacity: 1
    
}