.threeImage {
    width: 413px; /* 13 more than the photo width */
}

    .threeImage:nth-child(3n+0) {
        width: 426px; /* 6 more than the photo width */
        padding-left: 1px;
    }

#productSquares .threeImage {
    width: 426px; /* 6 more than the photo width */
    height: 295px; /* 6 more than the photo height */
    padding: 0;
}

.square {
    border: 5px solid black;
}