title: How to center div vertically in Bootstrap 4?
body: <p>I started work with bootstrap 4 and trying to create some basic layout. According to the <a href="https://getbootstrap.com/docs/4.0/layout/grid/#vertical-alignment" rel="nofollow noreferrer">bootstrap 4 docs</a>, I can align block elements vertically by applying class <code>align-items-center</code> to them.</p>
  
  <p>I tried to do the a <a href="https://codepen.io/anon/pen/JMvyJd" rel="nofollow noreferrer">basic example</a> on codepen, but div's are not positioned on center vertically.</p>
  
  <p>What I'm doing wrong?</p>