title: How to stretch width to 100% of scrollable area?
body: <p>I'd like to stretch the red div to 100% of the scrollable area, i.e. to the have blue's width but without hard coding red's width.</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>.outer {
    overflow: auto;
  }
  
  .blue {
    width: 200em;
    background: blue;
  }
  
  .red {
    width: 100%;/*does not work */
    background: red;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="outer"&gt;
    &lt;div class="blue"&gt;
      Test
    &lt;/div&gt;
    &lt;div class="red"&gt;
      Test
    &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="https://codepen.io/anon/pen/bxqEMy" rel="nofollow noreferrer">https://codepen.io/anon/pen/bxqEMy</a></p>