JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <div class="grid">
    <h1 class="grid_item">300 px row, 1fr column</h1>
    <h1 class="grid_item">300 px row, 1fr column</h1>
    <h1 class="grid_item">300 px row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">100 px row, 1fr column </h1>
    <h1 class="grid_item">100 px row, 1fr column </h1>
    <h1 class="grid_item">100 px row , 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
    <h1 class="grid_item">1fr row, 1fr column</h1>
  </div>
</body>

CSS

*{box-sizing: border-box;}

.grid{
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  grid-template-rows: 300px 1fr 100px;
  grid-gap: 20px;
}

/*Aesthetic only can ignore*/
.grid_item{
  border: 1px solid rgb(0, 95, 197);
  border-radius: 3px;
  background-color: rgba(0, 95, 107, 0.8);
  padding: 0.2em;
}