title: Why isn't this element centering?
body: <p>I'm asking this for a class assignment I'm working on, and somehow I've broken CSS so bad that even my teacher is stumped. </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 {
    font-family: Georgia, serif;
    background: url("graphics/Background.png");
    margin: 5%;
  }
  
  h1 {
    text-align: center;
    padding: 0px 0px 20px 0px;
  }
  
  .panel {
    border: 3px solid black;
    width: 500px;
    height: 500px;
    margin: 20px;
  }
  
  #container {
    display: flex;
    align-content: space-between;
    justify-content: center;
    background-color: red;
    flex-direction: column;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;h1&gt;Sunday Funnies&lt;/h1&gt;
  &lt;div id="container"&gt;
    &lt;img class="panel" src="Graphics/placeholder.png"&gt;
    &lt;img class="panel" src="Graphics/placeholder.png"&gt;
  &lt;/div&gt;
  &lt;/div&gt;
  
  ```</code></pre>
  </div>
  </div>
  </p>
  
  <p>This is what I have after my professor did some tinkering to try and figure out what was going on. </p>