JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="a">
    <div class="b"></div>
  </div>

  <div class="b">
    <div class="a"></div>
  </div>
</div>

SCSS

div {
  position: relative;
}

.container > div {
  float: left;
  
  background-color: red;
  width: 150px;
  height: 50px;
  z-index: 10;
  
  &:before {
    content: '';
    display: block;
    position: absolute;
    height: 100%;
    width: 100%;
    background-color: red;
    z-index: 7;
    top: 10px;
  }
}

.a > .b,
.b > .a {
  z-index: 5;
  position: absolute;
  width: 100%;
  height: 100%;
  background-color: teal;
}

.a + .b {
  margin-left: 20px
}