<div class="wrapper">
  <div class="box">1</div>
  <div class="box">2</div>
  <div class="box">3</div>
  <div class="box">4</div>
  <div class="box">5</div>
  <div class="box">6</div>
  <div class="box">7</div>
  <div class="box">8</div>
  <div class="box">9</div>
  <div class="box">10</div>
  <div class="box">11</div>
  <div class="box">12</div>
</div>
body {
  margin: 40px;
}

.box {
  background-color: #444;
  color: #fff;
  border-radius: 5px;
  padding: 20px;
  font-size: 150%;
}

.box:nth-child(even) {
  background-color: #ccc;
  color: #000;
}

.wrapper {
  width: 600px;
  display: grid;
  grid-gap: 10px;
  grid-template-columns: repeat(6, 100px);
  grid-template-rows: 100px 100px 100px;
  grid-auto-flow: column;
}

External CSS

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External JavaScript

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