CSS grid-auto-flow Explained

CSS grid-auto-flow Explained by Wes Bos

HTML

<link rel="stylesheet" href="https://cdn.rawgit.com/wesbos/css-grid/master/assets/style.css">
<div class="container">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
  <div class="item">3</div>
</div>

CSS

.container {
  display: grid;
  grid-gap: 20px;
  grid-template-columns: 400px 200px;
  grid-auto-flow: column;
  grid-auto-columns: 200px;
}