title: Grid item collapsing on smaller screen size
body: <p>I have a set of children inside a <code>display: grid</code> container - each child is numbered. At the 600px breakpoint, child <code>4</code> completely loses composure and deflates to its inner content size. Why doesn't <code>4</code> hop on down below <code>3</code>?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.box {
    background: yellow;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 48px;
    font-weight: bold;
  }
  
  .box.md {
    grid-column: span 2;
  }
  
  .box.lg {
    grid-column: span 2;
    grid-row: span 2;
  }
  
  .container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    grid-auto-rows: 240px;
    grid-auto-flow: dense;
    grid-gap: 8px;
  }
  
  @media (max-width: 920px) {
    max-width: 800px;
  }
  
  @media (max-width: 600px) {
    grid-auto-rows: 120px;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="container"&gt;
    &lt;div class="box lg"&gt;1&lt;/div&gt;
    &lt;div class="box md"&gt;2&lt;/div&gt;
    &lt;div class="box sm"&gt;3&lt;/div&gt;
    &lt;div class="box sm"&gt;4&lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="https://jsfiddle.net/amw273vq/" rel="nofollow noreferrer">https://jsfiddle.net/amw273vq/</a></p>