body {
  overflow: hidden;
  position: absolute;
  width: 100%;
  height: 100dvh;
}
div {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 1em;
  height: 1em;
  margin: -.5em 0 0 -.5em;
  font-size: 20px;
  border-radius: 1em;
  background-color: currentColor;
}