.demo-card:nth-child(4),
.demo-card:nth-child(5) {
  grid-column: span 6;
}

@media (max-width: 900px) {
  .demo-card:nth-child(4),
  .demo-card:nth-child(5) {
    grid-column: span 1;
  }
}

@media (max-width: 620px) {
  .demo-card:nth-child(4),
  .demo-card:nth-child(5) {
    grid-column: 1;
  }
}