实现代码如下所示：
<!doctype html>
<html class=no-js>
<head>
<meta charset=utf-8>
<meta http-equiv=X-UA-Compatible content=IE=edge>
<meta name=description content=>
<meta name=keywords content=>
<meta name=viewport content=width=device-width, initial-scale=1>
<title>模态窗口</title>
<link re
