title: Why isn't my flex item aligning in the center?
body: <p>I am trying to center a red box in the middle of the page.</p>
  
  <p>I have set the flex container to 100% in height, and have also set the html,body to 100%, and it still does not align center. </p>
  
  <p>Can anyone please help me understand why its not working? Thanks!</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>html, body {
    height: 100%;
  }
  .flex-container {
    display: flex;
    flex-flow: column;
    justify-content: center;
    height: 100%;
  }
  .box {
    flex: 0 0 100px;
    background: red;
    width: 100px;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class='flex-container'&gt;
      &lt;div class='box'&gt;&lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>