সিএসএস z-index

<!DOCTYPE html>
<html>
<head>
<style>
.tomato,
.orange {
  position: absolute;
  width: 100px;
  height: 100px;
}

.tomato {
  background: tomato;
  z-index: 1;
}

.orange {
  background: orange;
  left: 50px;
  top: 50px;
}
</style>
</head>
<body>

<div class="tomato"></div>
<div class="orange"></div>

</body>
</html>