title: Vertically centering text inside flexbox item
body: <p>I want the flex items to take full height, but the content inside them to be vertically centred.</p>
  
  <p><code>justify-content: centre</code> doesn't work, and <code>align-self: centre</code> on the item itself shrinks its height to its own content, while I want all items to be the same height.</p>
  
  <p>In this example I want the numbers to be vertically centred: <a href="http://codepen.io/ilyador/pen/ogYbWO?editors=110" rel="noreferrer">http://codepen.io/ilyador/pen/ogYbWO?editors=110</a></p>
  
  <p><div class="snippet" data-lang="js" data-hide="true" data-console="true" data-babel="false">
  <div class="snippet-code snippet-currently-hidden">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.flex-container {
    padding: 0;
    margin: 0;
    list-style: none;
    display: flex;  
  }
  
  .flex-item {
    flex: 1 1;
    background: tomato;
    padding: 5px;
    margin-top: 10px;
    color: white;
    font-weight: bold;
    font-size: 3em;
    text-align: center;
    border: solid 1px red;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;ul class="flex-container"&gt;
    &lt;li class="flex-item"&gt;1fbdms s s sdj dfkg kjfg dkfj gdfjkgdfkj gdfkjg dfkjgdkhdfjk gkjdfkjdfgdfg jkdfgdfjkgk &lt;/li&gt;
    &lt;li class="flex-item"&gt;2&lt;/li&gt;
    &lt;li class="flex-item"&gt;3&lt;/li&gt;
    &lt;li class="flex-item"&gt;4&lt;/li&gt;
    &lt;li class="flex-item"&gt;5&lt;/li&gt;
    &lt;li class="flex-item"&gt;6&lt;/li&gt;
  &lt;/ul&gt;</code></pre>
  </div>
  </div>
  </p>