vscode编辑
<!DOCTYPE html>
<html lang="en">
<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>Document</title>
<style>
.shadow{
position: fixed;
top: 0;
bottom: 0;
left: 0;
right: 0;
background-color:rgba(0,0,0,0.5);
z-index: 80;
}
.mode{
position: fixed;
height: 400px;
width: 400px;
background-color: white;
z-index: 100; /*数值越大，越在上层显示*/
left: 50%; /*按照窗口宽度的50%来移动*/
top: 50%; /*按照窗口高度的50%来移动*/
margin-top: -200px;
margin-left: -200px;/*正的相当于距离左边200px，负号相当于右边了 */
}
</style>
</head>
<body>
<div>
<h1>
我在测试
</h1>
</div>
<div class="mode"></div>
<div class="shadow"></div>
</body>
</html>