styles.css

#gallery {
    line-height: 0;
    -webkit-column-count: 5;
    /* split it into 5 columns */
    -webkit-column-gap: 5px;
    /* give it a 5px gap between columns */
    -moz-column-count: 5;
    -moz-column-gap: 5px;
    column-count: 2;
    column-gap: 5px;
}

#gallery img {
    width: 100% !important;
    height: auto !important;
    margin-bottom: 5px;
    /* to match column gap */
    filter: grayscale(100%);
}

#gallery img:hover {
    filter: none;
}

@media (max-width: 1200px) {
    #gallery {
        -moz-column-count: 1;
        -webkit-column-count: 1;
        column-count: 1;
    }
}

@media (max-width: 1000px) {
    #gallery {
        -moz-column-count: 1;
        -webkit-column-count: 1;
        column-count: 1;
    }
}

@media (max-width: 800px) {
    #gallery {
        -moz-column-count: 1;
        -webkit-column-count: 1;
        column-count: 1;
    }
}

@media (max-width: 400px) {
    #gallery {
        -moz-column-count: 1;
        -webkit-column-count: 1;
        column-count: 1;
    }
}