Demo: CSS grid-auto-columns

<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>

.grid-container {
  display: grid;
  grid-template-columns: repeat(2, 100px);
  grid-auto-columns: 150px;
  grid-auto-flow: column;
  grid-gap: 10px;
  background-color: #f0f0f0;
  padding: 10px;
}

.grid-item {
  background-color: #4CAF50;
  color: white;
  padding: 20px;
  text-align: center;
  border: 1px solid #333;
}

// No JavaScript required for this demo