<div class="box">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
  <div class="item">4</div>
  <div class="item">5</div>
  <div class="item">6</div>
  <div class="item">7</div>
  <div class="item">8</div>
  <div class="item">9</div>
  <div class="item">10</div>
  <div class="item">11</div>
  <div class="item">12</div>
</div>
.box {
  display: grid;
  grid: auto-flow 20vh / repeat(3, 30vw);
  grid-gap: 10px;
}

.box .item {
  background-color: #eee;
  color: #666;
  font-weight: 700;
  font-size: 4vw;
  padding: 10px;
  box-shadow: 0 0 2px 0 #000;
  text-align: center;
  padding-top: 25%;
}

External CSS

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External JavaScript

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