css 遮罩层

<!DOCTYPE html>
<html lang="en">
<head>
	<meta name="viewport" content="width=device-width, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no">
	<meta charset="UTF-8">
	<title>document</title>
	<style>
		*{margin:0;padding:0;}
		._mask{position: fixed;top: 0;bottom: 0;left: 0;right: 0;z-index: 100;background: rgba(0, 0, 0, 0.4);}
	</style>
</head>
<body>
	<div class="_mask"></div>
</body>
</html>

　　

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原文地址：https://www.cnblogs.com/lzs-888/p/6305661.html