.photo-row {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;

  width: 80%;
  max-width: 1000px;
  margin: 0 auto;       /* centres the whole row */
}

.photo-row img {
  width: 100%;
  height: auto;
  display: block;
}