<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>遮罩层样式</title>
<style type="text/css">
#maskDiv {
width: 100%;
height: 100%;
background: rgba(0, 0, 0, .5);
position: fixed;
left: 0;
top: 0;
z-index: 999;
display: block;
}
</style>
</head>
<body>
<div id="maskDiv"></div>
</body>
</html>
参考博客：css-弹窗遮罩层_cswan~~的博客-CSDN博客_css弹窗遮罩