代码示例:(标识:cssref_anim_z-index)
<!DOCTYPE html>
<html>
<head>
<style> 
div {position: absolute;}

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

div#myBox {
  opacity: 1;
  background-color: coral;
  z-index: 1;
  animation: mymove 5s infinite linear;
}

@keyframes mymove {
  50% {z-index: 5;}
}
</style>
</head>
<body style="position:absolute">

<h1>z-index 的动画效果:</h1>

<p>逐渐将 "myBox" 的 z-index 属性从 1 改为 5,然后再改回 1:<p>
<div id="container">
  <div id="myBox">myBox</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>

<p><b>注释:</b>CSS 动画在 Internet Explorer 9 以及更早版本中不起作用。</p>

</body>
</html>
运行结果: