title: z-index not working when transforming both psuedo element and parent
body: <p>Current I am trying to translate a parent element 10px on both the X &amp; Y axis while transforming an <code>::after</code> the equal amount in the other directions (this is to simulate the experience of the pseudo element moving nowhere). I expected this to be fairly trivial, however, the <code>::after</code> does not want to remain behind it's parent while being transformed.
  I assumed making a new stacking context would work, and I've never run into this issue before (having years of CSS experience).</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>body {
    background-color: #FFF;
  }
  
  button {
    padding: .75rem 1rem;
    background-color: #eee;
    border: none;
    font-weight: 500;
    font-size: 1rem;
    position: relative;
    transition: ease all .15s;
  }
  
  button::after {
    content: '';
    position: absolute;
    z-index: -1;
    height: 100%;
    width: 100%;
    background-color: #000;
    top: 0;
    left: 0;
    transition: ease all .15s;
  }
  
  button:hover {
    transform: translate(-10px, -10px);
  }
  
  button:hover::after {
    transform: translate(10px, 10px);
  } </code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
    &lt;meta charset="utf-8"&gt;
    &lt;meta name="viewport" content="width=device-width"&gt;
    &lt;title&gt;Fun Button&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
    
    &lt;button type="button"&gt;Fun Button!&lt;/button&gt;
  
  &lt;/body&gt;
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>