知识点：
1、辅助类
2、响应式工具
3、字体图标
4、下拉菜单
1、辅助类
1）文本
<p class="text-muted">本行内容是减弱的</p>
<p class="text-primary">本行内容带有一个 primary class</p>
<p class="text-success">本行内容带有一个 success class</p>
<p class="text-info">本行内容带有一个 info class</p>
<p class="text-warning">本行内容带有一个 warning class</p>
<p class="text-danger">本行内容带有一个 danger class</p>
2）背景
<p class="bg-primary">bootstrap课程</p>
<p class="bg-success">bootstrap课程</p>
<p class="bg-info">bootstrap课程</p>
<p class="bg-warning">bootstrap课程</p>
<p class="bg-danger">bootstrap课程</p>
3）关闭按钮 close
<button class="close">×</button>
4）下拉式菜单 caret
<span class="caret"></span>
5）浮动 pull-left pull-right
<div class="pull-left">向左快速浮动</div>
<div class="pull-right">向右快速浮动</div>
6）清除浮动 clearfix
<div class="clearfix" style="background: #D8D8D8;border: 1px solid #000;padding: 10px;">
<div class="pull-left" style="background:#58D3F7;">向左快速浮动</div>
<div class="pull-right" style="background: #DA81F5;">向右快速浮动</div>
</div>
7）块级内容居中 center-block
<div class="row">
<div class="center-block" style="width:200px;background-color:#ccc;">
这是 center-block
</div>
</div>
8）显示、隐藏 show hide
<div class="row" style="padding: 91px 100px 19px 50px;">
<div class="show" style="width:300px;background-color:#ccc;">
这是 show class
</div>
<div class="hidden" style="width:200px;background-color:#ccc;">
这是 hide class
</div>
</div>
9）屏幕阅读器和键盘导航 .sr-only 来把元素对所有设备隐藏，除了屏幕阅读器 .sr-only-focusable
<div class="row" style="padding: 91px 100px 19px 50px;">
<form class="form-inline" role="form">
<div class="form-group">
<label class="sr-only" for="email">Email 地址</label>
<input type="email" class="form-control" placeholder="Enter email">
</div>
<div class="form-group">
<label class="sr-only" for="pass">密码</label>
<input type="password" class="form-control" placeholder="Password">
</div>
</form>
</div>
<a class="sr-only sr-only-focusable" href="#content">Skip to main content</a>
2、响应式工具
1）visible-xs visible-sm visible-md visible-lg
hidden-xs hidden-sm hidden-md hidden-lg
以超小屏幕（xs）为例，可用的 .visible-*-* 类是：visible-xs-block、visible-xs-inline 和 visible-xs-inline-block。
2）visible-print-block visible-print-inline visible-print-inline-block 浏览器隐藏 打印机可见
hidden-print 浏览器可见 打印机隐藏
visible-print
<div class="container" style="padding: 40px;">
<div class="row">
<div class="col-xs-6 col-sm-3" style="background-color: #dedef8;border:1px solid #000;">
<span class="hidden-xs">特别小型</span>
<span class="visible-xs">✔ 在特别小型设备上可见</span>
</div>
<div class="col-xs-6 col-sm-3" style="background-color: #dedef8;border:1px solid #000;">
<span class="hidden-sm">小型</span>
<span class="visible-sm">✔ 在小型设备上可见</span>
</div>
<div class="col-xs-6 col-sm-3" style="background-color: #dedef8;border:1px solid #000;">
<span class="hidden-md">中型</span>
<span class="visible-md">✔ 在中型设备上可见</span>
</div>
<div class="col-xs-6 col-sm-3" style="background-color: #dedef8;border:1px solid #000;">
<span class="hidden-lg">大型</span>
<span class="visible-lg">✔ 在大型设备上可见</span>
</div>
</div>
</div>
3、字体图标
用法：<span class="glyphicon glyphicon-search"></span>
4、下拉菜单
1）基本的下拉菜单
<div class="dropdown">
<button class="btn btn-default dropdown-toggle" data-toggle="dropdown">Dropdown <span class="caret"></span></button>
<ul class="dropdown-menu">
<li><a href="">Html</a></li>
<li><a href="">Javascript</a></li>
<li><a href="">jQuery</a></li>
<li><a href="">html5+css3</a></li>
</ul>
</div>
2）对齐
dropdown-menu-right
3）标题 不要加超链接
<ul class="dropdown-menu">
...
<li class="dropdown-header">Dropdown header</li>
...
</ul>
4）分隔线
<ul class="dropdown-menu">
...
<li class="divider"></li>
...
</ul>
5）禁用的菜单项
<ul class="dropdown-menu" aria-labelledby="dropdownMenu4">
<li><a href="#">Regular link</a></li>
<li class="disabled"><a href="#">Disabled link</a></li>
<li><a href="#">Another link</a></li>
</ul>
6）让菜单默认显示
<div class="dropdown open">