<div class="height">
  <h2>Make a <code>&lt;div&gt;</code> 100% Height of Browser Window (Using Flexbox)</h2>
  
  <p>The element with the blue backround stretches to fill its parent no matter the size of the window. This uses flexbox to achieve this effect.</p>

</div>

html, body {
  height: 100%;
}

body {
  font-family: Arial, sans-serif;
  font-size: 20px;
  display: flex;
}

.height {
  text-align: center;
  margin: 0 auto;
  max-width: 560px;
  background: lightblue;
  padding: 0 20px;
  flex-grow: 1;
}

p {
  text-align: left;
  padding: 0 20px;
}

code {
  color: firebrick;
}