title: background-attachment : fixed; not working with background-position
body: <p>I have made a <a href="https://codepen.io/anon/pen/qjWvdm" rel="nofollow noreferrer">codepen</a> to explain my problem:</p>
  
  <ul>
  <li>When the user scroll, the blue images should follow the user scroll</li>
  <li>The blue images should be stuck on the opposite side of the aside parts (right for the left one | left for the right one)</li>
  </ul>
  
  <p>The pb is that </p>
  
  <blockquote>
    <p><code>background-attachment : fixed;</code></p>
  </blockquote>
  
  <p>isn't working this the css rule </p>
  
  <blockquote>
    <p><code>background-position: left 0px;</code></p>
  </blockquote>
  
  <p>Someone can help me by forking the codepen to show me a working implementation ?</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>.wrapper {
    display: flex;
  }
  
  main {
    background-color: red;
    height: 1000px;
    max-width: 992px;
    width: 100%;
  }
  
  aside {
    min-width: 150px;
    background-color: green;
  }
  
  .left {
    background-image: url(http://www.bodyacademy.fr/wp-content/uploads/2015/02/Bande_bleu1-100x500.png);
    background-repeat: no-repeat;
    background-position: right 0px;
    /*background-attachment: fixed; Doesn't work*/
  }
  
  .right {
    background-image: url(http://www.bodyacademy.fr/wp-content/uploads/2015/02/Bande_bleu1-100x500.png);
    background-repeat: no-repeat;
    background-position: left 0px;
    /*background-attachment: fixed; Doesn't work*/
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="wrapper"&gt;
    &lt;aside class="left"&gt;&lt;/aside&gt;
    &lt;main&gt;&lt;/main&gt;
    &lt;aside class="right"&gt;&lt;/aside&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>