div.photo-gallery {
    display: block;
}

div.photo-gallery div.photo {
    display: inline-block;
    margin: 15px/*40px*/;
    box-sizing: content-box;
    width: 75px/*150px*/;
    /*box-shadow: 3px 3px 3px 0 gray;*/
    border: 4px solid transparent;
}

div.photo-gallery div.photo img {
    width: 75px/*150px*/;
}