#photos {
  column-count: 4;
  column-gap: 8px;
  line-height: 0; /* remove whitespace below image */
  padding-bottom: 39px;
  width: 100%;
}

#photos img {
  border: 5px solid rgba(255,255,255,0);
  border-radius: 5px;
  height: auto;
  transition: 0.3s;
  width: 100%;
}

#photos img:hover {
  border-color: rgba(255,255,255,0.9);
}

/* smaller screens */

@media (max-width: 1000px) {
  #photos { column-count: 3; }
}

@media (max-width: 768px) {
  #photos { column-count: 2; }
}

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