图（1）初始图
图（2）点击按钮后
代码如下：
<!DOCTYPE HTML> <html> <head> <meta charset="UTF-8" /> <title></title> <style> #mask { position: absolute; top: 0; left: 0; width: 100%; height: 100%; z-index: 999; background: #666; opacity: 0.5; filter: alpha(opacity=50)-moz-opacity: 0.5; display: none; } .popup { position: absolute; left: 50%; width: 600px; height: 200px; background: #fff; z-index: 1000; border: 1px solid #333; display: none; } .btn_close { position: absolute; top: 5px; right: 5px; } </style> </head> <body> <button>遮罩层</button> <div></div> <div> <button>x</button> </div> <script src="https://cdn.bootcss.com/jquery/3.1.1/jquery.js"></script> <script> $(function() { $('.btn_show').click(function() { $('#mask').css({ display: 'block', height: $(document).height() }) var $Popup = $('.popup'); $Popup.css({ left: ($('body').width() - $Popup.width()) / 2+ 'px', top: ($(window).height() - $Popup.height()) / 2 + $(window).scrollTop() + 'px', display: 'block' }) }) $('.btn_close').click(function() { $('#mask,.popup').css('display', 'none'); }) }) </script> </body> </html>