title: Vertical align on full height page using flexbox
body: <p>I am trying to create simple page that has header with navbar that is separated by content area. I am unable to force div <code>#cover</code> to be aligned in center vertically. I want my design to be responsive so I do not want to specify width on the parent div <code>content</code>.
  I know I can use <code>flex: 1</code> to fill the rest of the area but I tried that and it does not work for me.</p>
  
  <p>Please see here: <a href="http://codepen.io/anon/pen/wMNjyd" rel="nofollow">Codepen</a></p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.site-content {
    display: flex;
    flex-direction: column;
  }
  .navbar {
    display: flex;
    justify-content: space-between;
  }
  nav ul {
    display: flex;
    list-style-type: none;
  }
  li {
    margin: 0 10px;
  }
  .content {
    display: flex;
    flex: 1;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="site-content"&gt;
    &lt;div class="navbar"&gt;
      &lt;div class="title"&gt;TitLe&lt;/div&gt;
      &lt;nav&gt;
        &lt;ul&gt;
          &lt;li&gt;link1&lt;/li&gt;
          &lt;li&gt;link2&lt;/li&gt;
          &lt;li&gt;link3&lt;/li&gt;
        &lt;/ul&gt;
      &lt;/nav&gt;
    &lt;/div&gt;
    &lt;div class="content"&gt;
      &lt;div id="cover"&gt;
        Lorem ipsum
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>