<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title></title> <style> * { margin: 0px; padding: 0px; } .login { width: 100px; height: 30px; font-size: 25px; line-height: 30px; border: 1px solid black; text-align: center; background-color: darkcyan; color: white; } .login:hover { cursor: pointer; background-color: greenyellow; } .mask { width: 100%; background-color: black; opacity: 0.5; position: absolute; top: 0px; left: 0px; z-index: 90; } .log-div { width: 500px; height: 300px; background-color: white; position: fixed; /*top: 30%;*/ /*left: 30%;*/ z-index: 99; } </style> </head> <body> <div class="mask" hidden></div> <div class="log-div" hidden="hidden"></div> <div class="login">登 录</div> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> <p>123</p> </body> </html> <script> var mask = document.getElementsByClassName("mask")[0]; var login = document.getElementsByClassName("log-div")[0]; var btn = document.getElementsByClassName("login")[0]; var clientWidth = document.body.clientWidth; var clientHeight = document.documentElement.clientHeight; login.style.left = clientWidth / 2 - 250 + "px"; login.style.top = clientHeight / 2 - 150 + "px"; mask.style.height = document.body.clientHeight + "px"; window.onresize = function() { var clientWidth = document.body.clientWidth; var clientHeight = document.documentElement.clientHeight; login.style.left = clientWidth / 2 - 250 + "px"; login.style.top = clientHeight / 2 - 150 + "px"; } btn.onclick = function(){ mask.removeAttribute("hidden"); login.removeAttribute("hidden"); } mask.onclick = function(){ mask.setAttribute("hidden",""); login.setAttribute("hidden","hidden"); } </script>