Demo: CSS grid-template

<div class='grid-container'>
  <div class='item1'>Item 1</div>
  <div class='item2'>Item 2</div>
  <div class='item3'>Item 3</div>
  <div class='item4'>Item 4</div>
</div>

.grid-container {
  display: grid;
  grid-template: 100px 200px / 1fr 2fr;
  gap: 10px;
}

.grid-container > .item1,
.grid-container > .item2,
.grid-container > .item3,
.grid-container > .item4 {
  background-color: lightblue;
  border: 1px solid blue;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
}

.item1 { background-color: lightcoral; }
.item2 { background-color: lightgreen; }
.item3 { background-color: lightgoldenrodyellow; }
.item4 { background-color: lightpink; }

// No JavaScript required for this demo