.gallery-item {
    position:relative;
    width:130px;
    float:right;
    background-color:#f0d700; /* yellow */
    margin-right:2.5em;
    margin-bottom:2.5em;
}

    .gallery-item img {
        display:block;
        max-width:100%;
        opacity:0.3;
    }
    
    .gallery-item:hover img {
        opacity:1;
        transition: opacity 1s;
    }
    
/*    .crop {
        position:absolute;
        top:0;
        left:0;
        opacity:1 !important;
        z-index: 2;
    }*/
    
    .gallery-item:nth-of-type(3n-2) {
        margin-right:0;
    }