Demo: CSS grid-auto-rows

<div class='grid-container'>
  <div class='grid-item'>Item 1</div>
  <div class='grid-item'>Item 2</div>
  <div class='grid-item'>Item 3</div>
  <div class='grid-item'>Item 4</div>
  <div class='grid-item'>Item 5</div>
  <div class='grid-item'>Item 6</div>
</div>

.grid-container {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-auto-rows: 100px;
  gap: 10px;
}

.grid-item {
  background-color: lightblue;
  border: 1px solid blue;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
}

// No JavaScript required for this demo