simple and nice images grid layout using flex only

image-grid-with-flex.css

#photos {
  display: flex;
  flex-wrap: wrap;
  flex-direction: row;
}

#photos div {
  flex: auto;
  width: 150px;
  margin: 5px;
  border: 1px solid #ddd;
}

#photos div img {
  width: 100%;
  height: auto;
}