1. 效果展示

2. 代码核心思路

3. 代码
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
<style>
.login-header {
width: 100%;
text-align: center;
height: 30px;
font-size: 24px;
line-height: 30px;
}
ul,
li,
ol,
dl,
dt,
dd,
div,
p,
span,
h1,
h2,
h3,
h4,
h5,
h6,
a {
padding: 0px;
margin: 0px;
}
.login {
display: none;
width: 512px;
height: 280px;
position: fixed;
border: #ebebeb solid 1px;
left: 50%;
top: 50%;
background: #ffffff;
box-shadow: 0px 0px 20px #ddd;
z-index: 9999;
transform: translate(-50%, -50%);
}
.login-title {
width: 100%;
margin: 10px 0px 0px 0px;
text-align: center;
line-height: 40px;
height: 40px