CSS Animatable z-index Property Example

<!DOCTYPE html>
<html>
<head>
<style> 
div {position: absolute;}

#container div {
  background-color: #ff0;
  border: 1px solid #333333;
  width: 100px;
  height: 100px;
  opacity: 0.5;
}

div#wrapper {
  opacity: 1;
  background-color: red;
  z-index: 1;
  animation: anim 5s infinite linear;
}

@keyframes anim {
  50% {z-index: 5;}
}
</style>
</head>
<body>

<h1>Animatable 'word-spacing' Property</h1>
<hr>
  
<p>Experience the changing z-index property.<p>

<div id="container">
  <div id="wrapper">Wrapper</div>
  <div style="top:20px;left:20px;z-index:1;">z-index 1</div>
  <div style="top:40px;left:40px;z-index:2;">z-index 2</div>
  <div style="top:60px;left:60px;z-index:3;">z-index 3</div>
  <div style="top:80px;left:80px;z-index:4;">z-index 4</div>
</div>

</body>
</html>