<div class="demo">
  CSS Variables
</div>

:root {
  --background: #212121;
  --text: white;
  --shadow: 10px 0 15px black;
}

html,
body {
  background-color: var(--background);
  color: var(--text);
  text-shadow: var(--shadow);
  
  display: table;
  height: 100%;
  width: 100%;
  font: 100 8vw 'Roboto';
  margin: 0;
}

.demo {
  display: table-cell;
  vertical-align: middle;
  text-align: center;
}