.spacer {
  height: 320px;
}

/* Medium devices (tablets, 768px and up) */
@media (min-width: 768px) {
  .spacer {
    height: 400px;
  }
}

/* Large devices (desktops, 992px and up) */
@media (min-width: 992px) {
  .spacer {
    height: 300px;
  }
}