body
  {
  background: linear-gradient(to right, #494949 0%,#878787 20%,#878787 80%,#494949 100%);
  }

.zentrierung
  {
  position: absolute;
  top: -9999px;
  bottom: -9999px;
  left: -9999px;
  right: -9999px;
  margin: auto;
  }

.preload
  {
  width: 1px;
  height: 1px;
  position: absolute;
  left: 1px;
  top: 1px;
  }