1.bootstrap中文官网
2.步骤
2.1复制基本模板代码
https://v3.bootcss.com/getting-started/#template
2.2复制页头代码
https://v3.bootcss.com/components/#page-header
2.3创建中间登录框部分div和底部div
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>登录界面
</title>
<!-- Bootstrap -->
<link href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<!-- 标题 -->
<div class="page-header">
<h1>XXXX信息系统登录界面</h1>
</div>
<!-- 中间登录框 -->
<div class="container-fluid">
<div class="row">
</div>
</div>
<!-- 页脚 -->
<div class="footer">
<p>©版权所有：XXXXX学院XX市XX大道XXX号</p>
<p>邮编：530001联系邮箱：xxxxxxx@163.com</p>
</div>
</div>
<!-- jQuery (Bootstrap 的所有 JavaScript 插件都依赖 jQuery，所以必须放在前边) -->
<script src="https://cdn.jsdelivr.net/npm/jquery@1.12.4/dist/jquery.min.js"></script>
<!-- 加载 Bootstrap 的所有 JavaScript 插件。你也可以根据需要只加载单个插件。 -->
<script src="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/js/bootstrap.min.js"></script>
</body>
</html>
2.4复制水平排列表单到中间登录框部分div
https://v3.bootcss.com/css/#forms-horizontal
2.5 调整样式（一个Html标签可以应用多个类样式，中间用空格隔开）
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>登录界面
</title>
<!-- Bootstrap -->
<script src="js/jquery-3.4.1.js"></script>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap.min.css" rel="stylesheet">
<style>
.bg{
height: 600px;
background-image:url(/images/bg.jpg);
background-size:cover;
}
.form{
padding: 40px;
margin-top: 175px;
background: rgba(255,255,255,0.2);
}
.footer{
height: 60px;
padding-top:20px;
font-size: 14px;
font-weight: bold;
text-align: center;
}
</style>
</head>
<body>
<div class="page-header">
<h1>XXXX信息系统登录界面</h1>
</div>
<div class="container-fluid">
<div class="row bg">
<div class="col-md-offset-6 col-md-4 col-sm-offset-3 col-sm-7 col-xs-offset-2 col-xs-8 col-lg-offset-6 col-lg-3 form">
<form class="form-horizontal" id="loginForm">
<div class="form-group">
<label for="username" class="col-sm-4 control-label">用户名</label>
<div class="col-sm-8">
<input type="text" class="form-control" id="username" placeholder="请输入用户名">
</div>
</div>
<div class="form-group">
<label for="password" class="col-sm-4 control-label">密码</label>
<div class="col-sm-8">
<input type="password" class="form-control" id="password" placeholder="请输入密码">
</div>
</div>
<div class="form-group">
<label for="validateCode" class="col-sm-4 control-label">验证码</label>
<div class="col-sm-4">
<input type="text" class="form-control" id="validateCode" placeholder="请输入验证码" >
</div>
<div class="col-sm-4">
<img src="images/yzm.jpg" alt="" width="75px" height="35px">
</div>
</div>
<div class="form-group">
<div class="col-sm-offset-2 col-sm-10">
<div class="checkbox">
<label>
<input type="checkbox">记住我
</label>
</div>
</div>
</div>
<div class="form-group">
<div class="col-sm-offset-2 col-sm-10">
<button type="button" id="submitBtn" class="btn btn-success" style=" 50%;">登录</button>
</div>
</div>
</form>
<span style="color: red;" id="tip"></span>
</div>
</div>
<div class="footer">
<p>©版权所有：XXXXX学院XX市XX大道XXX号</p>
<p>邮编：530001联系邮箱：xxxxxxx@163.com</p>
</div>
</div>
<!-- jQuery (Bootstrap 的所有 JavaScript 插件都依赖 jQuery，所以必须放在前边) -->
<script src="https://cdn.jsdelivr.net/npm/jquery@1.12.4/dist/jquery.min.js"></script>
<!-- 加载 Bootstrap 的所有 JavaScript 插件。你也可以根据需要只加载单个插件。 -->
<script src="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/js/bootstrap.min.js"></script>
</body>
</html>
3.运行效果图（一个简陋的登录界面）
