index.html

<div class="box">
</div>

oXYpoz.markdown

oXYpoz ('-' * 6)

A Pen by Captain Anonymous on CodePen.

License.

style.css

.box {
  position: absolute;
  margin: auto;
  width: 100px;
  height: 100px;
  background-color: red;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;

}