title: Can't make overflow-x work in a full width flexbox column
body: <p>I'm trying to create a 2 column layout with flexbox. One is fixed width on the side and the other one (main column) fills the remaining space.</p>
  
  <p>It was working until I put some contents wider than the screen with a <code>overflow-x: scroll</code> parent. Now this wide content is not limited by its scroller parent.</p>
  
  <p>Here is the sample:
  <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>.container {
    display: flex;
  }
  .container .col-main {
    background: gold;
    flex: 1 1 100%;
  }
  .container .col-side {
    background: cornflowerblue;
    flex: 0 0 15em;
  }
  
  .slider-container {
    overflow-x: scroll;
  }
  .slider-container .slider {
    background: repeating-linear-gradient(45deg, darkseagreen, darkseagreen 10px, dimgray 10px, dimgray 20px);
    width: 150em;
    height: 10em;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="container"&gt;
    &lt;div class="col-main"&gt;
  
      &lt;div class=slider-container&gt;
        &lt;div class="slider"&gt;
          Foo
        &lt;/div&gt;
      &lt;/div&gt;
  
    &lt;/div&gt;
    &lt;div class="col-side"&gt;
      Side
    &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>It should be rendered like this:
  <a href="https://i.stack.imgur.com/V97Qz.png" rel="noreferrer"><img src="https://i.stack.imgur.com/V97Qz.png" alt="enter image description here"></a></p>