<div class="container">
  <span class="demo center">Thing that should be centered on the page</span>
</div>
.container {
  width: 100vw;
  height: 100vh;
}

.center {
  bottom: 0;
	height: 100px;
	left: 0;
	margin: auto;
	position: absolute;
	right: 0;
	top: 0;
	width: 100px;
}

.demo {
  background-color: gray;
  color: white;
  padding: 0.25em;
}

External CSS

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External JavaScript

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