CodePen Embed - z-index and stacking context

<div class="poem">
  遥想公瑾当年，小乔初嫁了，雄姿英发。羽扇纶巾，谈笑间，樯橹灰飞烟灭。
  <div class="author">
    <span>苏轼</span>
  </div>
</div>

poem {
  background: red;
}
.author {
  position: absolute;
  top: 5px;
  left: 0;
  background: green;
}

.author span {
  z-index: -1;
}

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