Vertically centering a flex item works in Chrome but not Firefox
<p>I've written this simple code for centering my inner <code>div</code>:</p>

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<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div style="display: flex;align-items: center;width: 100%;height: 600px;background-color: gray;"&gt;
  &lt;div style="background-color: white;width: 100px;height: 300px;position: absolute;"&gt;&lt;/div&gt;
&lt;/div&gt;</code></pre>
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<p>And it works fine in Chromium. but not in Firefox.</p>

<p>In Firefox the inner div is not centered.</p>

<p>Firefox:</p>

<p><a href="https://i.stack.imgur.com/JFoLG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JFoLG.png" alt="enter image description here"></a></p>

<p>Chromium:</p>

<p><a href="https://i.stack.imgur.com/qHEWz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qHEWz.png" alt="enter image description here"></a></p>

<p>I need the inner div to remain absolutely positioned.</p>