JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <h1>Vertical aligned
    <button>I am a button</button>
  </h1>
</div>
<div class="container">
  <h1>Vertical aligned</h1>
</div>

CSS

html, body {
  margin: 0;
  height: 100%;
  width: 100%;
}
.container {
  height: 100%;
  width: 50%;
  float: left;
  
  text-align: center;
  display: flex;
  justify-content: center;
  flex-direction: column;
}