其实我们不用下载bootstrap也可以使用它：

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base.html

<!DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <!-- 上述3个meta标签*必须*放在最前面，任何其他内容都*必须*跟随其后！ -->
    <title>Bootstrap 101 Template</title>

    <!-- Bootstrap -->
    <link rel="stylesheet" href="http://cdn.bootcss.com/bootstrap/3.3.4/css/bootstrap.min.css">
    
  </head>
  <body>
    <h1>你好，bootstrap！</h1>

    <!-- jQuery (necessary for Bootstrap's JavaScript plugins) -->
    <script src="http://cdn.bootcss.com/jquery/1.11.2/jquery.min.js"></script>
    <!-- Include all compiled plugins (below), or include individual files as needed -->
    <script src="http://cdn.bootcss.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
  </body>
</html>

base.html中已经引入了bootstrap，将其保存，我们就可以使用bootstrap提供的样式了。

字体图标

bootstrap默认提供了二百多个图标。我们可以通过span标签来使用这些图标：

    <h3>图标</h3>   
    <span class="glyphicon glyphicon-home"></span>
    <span class="glyphicon glyphicon-signal"></span>
    <span class="glyphicon glyphicon-cog"></span>
    <span class="glyphicon glyphicon-apple"></span>
    <span class="glyphicon glyphicon-trash"></span>
    <span class="glyphicon glyphicon-play-circle"></span>
    <span class="glyphicon glyphicon-headphones"></span>

按钮

　　<button></button>标签用于创建按钮，bootstrap提供了丰富的按钮样式。

    <h3>按钮</h3>
    <button type="button" class="btn btn-default">按钮</button>
    <button type="button" class="btn btn-primary">primary</button>
    <button type="button" class="btn btn-success">success</button>
    <button type="button" class="btn btn-info">info</button>
    <button type="button" class="btn btn-warning">warning</button>
    <button type="button" class="btn btn-danger">danger</button>
    
    <h3>按钮尺寸</h3>
    <button type="button" class="btn btn-default">按钮</button>
    <button type="button" class="btn btn-primary btn-lg">primary</button>
    <button type="button" class="btn btn-success btn-sm">success</button>
    <button type="button" class="btn btn-info btn-xs">info</button>

    <h3>把图标显示在按钮里</h3>
    <button type="button" class="btn btn-default"><span class="glyphicon glyphicon-home"></span>&nbsp;&nbsp;按钮</button>

　　按钮除了有默认的大小外，bootstrap还提供三个参数来调整按钮的大小，分别是：btn-lg、btn-sm和btn-xs。

下拉菜单

　　下拉菜单是最常见的交互之一，bootstrap提供了漂亮的样式。

     <h3>下拉菜单</h3>
    <div class="dropdown">
      <button class="btn btn-primary dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown" aria-expanded="true">
        Dropdown
        <span class="caret"></span>
      </button>
      <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
        <li role="presentation"><a role="menuitem" tabindex="-1" href="#">Action</a></li>
        <li role="presentation"><a role="menuitem" tabindex="-1" href="#">Another action</a></li>
        <li role="presentation"><a role="menuitem" tabindex="-1" href="#">Something else here</a></li>
        <li role="presentation"><a role="menuitem" tabindex="-1" href="#">Separated link</a></li>
      </ul>
    </div>

输入框

　　通过<input></input>标签去创建输入框。

    <h3>输入框</h3>
    <div class="input-group">
      <span class="glyphicon glyphicon-user"></span>
      <input type="text" placeholder="username">
    </div>

    <div class="input-group">
      <span class="glyphicon glyphicon-lock"></span>
      <input type="password" placeholder="password">
    </div>

导航栏

　　导航栏作为整个网站的指引必不可少。

    <h3>导航栏</h3>
    <nav class="navbar navbar-inverse navbar-fixed-top">
        <div id="navbar" class="navbar-collapse collapse">
          <ul class="nav navbar-nav">
            <li class="active"><a href="#">Home</a></li>
            <li><a href="#about">About</a></li>
            <li><a href="#contact">Contact</a></li>
            <li class="dropdown">
              <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">Dropdown <span class="caret"></span></a>
              <ul class="dropdown-menu" role="menu">
                <li><a href="#">Action</a></li>
                <li><a href="#">Another action</a></li>
                <li class="divider"></li>
                <li class="dropdown-header">Nav header</li>
                <li><a href="#">Separated link</a></li>
              </ul>
            </li>
          </ul>
        </div><!--/.nav-collapse -->
      </div>
    </nav>

表单

　　人与系统之间数据的传递都需要依靠表单来完成。比如注册/登录信息的提交，查询条件的提交等。用<form></form>标签来创建表单。

   <h3>表单</h3>
    <form>
    <div class="form-group">
      <span class="glyphicon glyphicon-user"></span>
      <input type="email" id="exampleInputEmail1" placeholder="Enter email">
    </div>
    <div class="form-group">
      <span class="glyphicon glyphicon-lock"></span>
      <input type="password" id="exampleInputPassword1" placeholder="Password">
    </div>
    <div class="form-group">
      <label for="exampleInputFile">File input</label>
      <input type="file" id="exampleInputFile">
      <p class="help-block">Example block-level help text here.</p>
    </div>
    <div class="checkbox">
      <label>
        <input type="checkbox"> Check me out
      </label>
    </div>
    <button type="submit" class="btn btn-default">Submit</button>
  </form>

警告框

　　警告框是系统向用户传达信息和提供指引的重要手段。没有针对警告框的标签，通过bootstrap所提供的样式可以瞬间制作出漂亮的警告框。

    <h3>警告框</h3>
    <div class="alert alert-warning alert-dismissible" role="alert">
       <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">&times;</span></button>
       <strong>Warning!</strong> Better check yourself, you're not looking too good.
    </div>
    <div class="alert alert-success" role="alert">
        <a href="#" class="alert-link">success!</a>
    </div>
    <div class="alert alert-info" role="alert">
        <a href="#" class="alert-link">info!</a>
    </div>
    <div class="alert alert-warning" role="alert">
        <a href="#" class="alert-link">warning!</a>
    </div>
    <div class="alert alert-danger" role="alert">
        <a href="#" class="alert-link">danger!</a>
    </div>

进度条

　　系统的处理过程往往需要用户等待，进度条可以让用户感知到系统的处理过程，从而增加容忍度。

    <h3>进度条</h3>
    <div class="progress">
      <div class="progress-bar" role="progressbar" aria-valuenow="70" aria-valuemin="0" aria-valuemax="100" style="width: 60%;">
        70%
      </div>
    </div>