re:从0开始的CSS之旅 18. z-index

1. z-index

z-index 属性用于设置元素的叠放层次，属性值可以为一个整数，整数值越大越优先显示

注意：z-index只对开启了定位的元素有效

示例如下：

<!DOCTYPE html>
<html lang="en">

<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>

	div {
		width: 200px;
		height: 200px;
	}
	
	.box1 {
		background-color: #c7edcc;
	
		position: relative;
		left: 50px;
		top: 100px;
	
		z-index: -2;
	}
	
	.box2 {
		background-color: #fde6e0;
	
		position: absolute;
		left: 150px;
		top: 150px;
	
		z-index: -1;
	}
	
	.box3 {
		background-color: #dce2f1;
	
		float: left;
	}
	
	.box4 {
		background-color: red;
		position: fixed;
		left: 125px;
		top: 225px;
	}
</head>

<body>
	<div class="box1">相对定位</div>
	<div class="box2">绝对定位</div>
	<div class="box3">浮动</div>
	<div class="box4">固定定位</div>
</body>

</html>