/* the actual CSS to make them evenly spaced: */

#image_grid {
    display: flex;
    justify-content: center; /* space-between */
    align-content: center; /* space-between */
    flex-direction: row;
    flex-wrap: wrap;
    margin-bottom: 40px;
}

#image_grid div {
    background: rgba(255, 255, 255, .1); /* when hovering over img, this color will show */
    padding:20px;
    height: 260px;
    width: 462px;
}

#image_grid div img {
    height: 100%;
    width: 100%;
    overflow: true;
    /* transitions */
    -o-transition:.3s ease-out;
    -ms-transition:.3s ease-out;
    -moz-transition:.3s ease-out;
    -webkit-transition:.3s ease-out;
    transition:.3s ease-out;
}

#image_grid img:hover {
    opacity: 0.6;
}