.holder.boxes .flex > div {
  width: 300px;
  height: 250px;
}

.holder.boxes .box .block-image {
  vertical-align: top;
  width: 300px;
  height: 250px;
  background-position: center center;
  background-repeat: no-repeat;
  background-size: 100%;
  position: relative;
}

@media (max-width: 970px) {
  .holder.boxes .flex > div {
    flex-basis: 300px;
    width: 300px;
    margin-bottom: 1em;
  }
  .holder.boxes .flex > div:last-of-type {
    margin-bottom: 0;
  }
}