如何使父元素在绝对定位的情况下复盖子元素

.parent {
  position: absolute;
  z-index: 1;
}

.child {
  position: absolute;
  z-index: 0;
}

<div class="container">
  <div class="child"></div>
  <div class="parent"></div>
</div>

.container {
  position: relative;
}

.parent {
  position: absolute;
}

.child {
  position: absolute;
}

.parent::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}