#grid-container {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 5px;
}
#grid-container div {
  padding: 20px;
  background: #CCCCCC;
}
#box-1 {
  grid-column: 1 / span 3;
}
#box-2 {
  grid-column: 1 / span 2;
  grid-row: 2 / span 2;
}