understanding_z-index.css

.container {
  width: 600px;
  height: 300px;
  background-color: burlywood;
  margin: auto;
  position: relative;
  z-index: 0;
  margin-top: 150px;
}

.container::before {
  content: "container before";
  background-color: rgba(179, 120, 120, 0.898);
  width: 100%;
  height: 100%;
  position: absolute;
  margin-top: -30px;
  margin-left: 30px;
}

.container::after {
  content: "container after";
  background-color: rgba(0, 0, 255, 0.816);
  width: 100%;
  height: 100%;
  position: absolute;
  margin-top: -60px;
  margin-left: 60px;
  z-index: 6;
}

.box {
  width: 400px;
  height: 60%;
  background-color: cadetblue;
  position: absolute;
  margin-top: 140px;
  margin-left: -60px;
  opacity: 0.9;
  z-index: 5;
}

.box::before {
  content: "box before";
  position: absolute;
  width: 100%;
  height: 60px;
  top: 0;
  left: 0;
  margin-top: 10px;
  margin-left: -80px;
  background-color: blueviolet;
  box-shadow: 0 0 10px black;
  z-index: 0;
}

.box::after {
  content: "box after";
  position: absolute;
  width: 100%;
  height: 60px;
  margin-top: 30px;
  margin-left: -60px;
  top: 20%;
  left: 0;
  background-color: coral;
  box-shadow: 0 0 10px black;
  z-index: 7;
}