#gallery {
    line-height: 0;
    column-count: 4;
    column_gap: 5px;
}

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

@media (max-width: 1200px) {
   #gallery {
    -moz-column-count:    3;
    -webkit-column-count: 3;
    column-count:         3;
   }
}

@media (max-width: 900px) {
   #gallery {
    -moz-column-count:    2;
    -webkit-column-count: 2;
    column-count:         2;
   }
}


@media (max-width: 500px) {
   #gallery {
    -moz-column-count:    1;
    -webkit-column-count: 1;
    column-count:         1;
   }
}