title: Vertically center a div inside another div
body: <p>I'm trying to <code>vertical-align: middle</code> a div inside another div, but for some reason it's not working properly. What am I doing wrong?</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>#wrapper {
  border: 1px solid red;
  width: 500px;
  height: 500px;
  }
  #block {
  border: 1px solid blue;
  width: 500px;
  height: 250px;
  vertical-align: middle;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div id = 'wrapper'&gt; 
  &lt;div id = 'block'&gt; I'm Block &lt;/div&gt;
  &lt;div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><b> PS: </b> This is just an example, so no, I don't actually know the actual width and height of the divs, as they are dynamic, according to their contents, so please no margin-top: 125px, or padding-top: 125px answers, or answers like that.</p>