将一个div水平堆叠在另一个div上

<div class="container">
  <div class="div1"></div>
  <div class="div2"></div>
</div>

.container {
  position: relative;
}

.div1 {
  position: absolute;
  top: 0;
  left: 0;
  width: 200px;
  height: 200px;
  background-color: red;
  z-index: 1;
}

.div2 {
  position: absolute;
  top: 50px;
  left: 50px;
  width: 200px;
  height: 200px;
  background-color: blue;
  z-index: 2;
}