.container {
  background: #000;
  bottom: 0;
  left: 0;
  position: fixed;
  right: 0;
  top: 0;
  
  span {
    color: #0f0;
    font-size: 10rem;
    left: 50%;
    position: absolute;
    transform: translate(-50%, -50%);
    top: 50%;
  }
}