BootStrap初学，碰到CSS样式问题。

这两天开始学习bootstrap，下载的是最新的3.3.7版本。
在一个bootstrap中文网看到一个例子。代码是这样的：
<!DOCTYPE html>

Bootstrap, from Twitter

<!-- Le styles -->
<link href="../bootstrap/2.3.1/css/bootstrap.css" rel="stylesheet">
<style>
  body {
    padding-top: 60px; /* 60px to make the container go all the way to the bottom of the topbar */
  }
</style>
<link href="../bootstrap/2.3.1/css/bootstrap-responsive.css" rel="stylesheet">

<!-- HTML5 shim, for IE6-8 support of HTML5 elements -->
<!--[if lt IE 9]>
  <script src="../bootstrap/assets/js/html5shiv.js"></script>
<![endif]-->

<!-- Fav and touch icons -->
<link rel="apple-touch-icon-precomposed" sizes="144x144" href="../assets/ico/apple-touch-icon-144-precomposed.png">
<link rel="apple-touch-icon-precomposed" sizes="114x114" href="../assets/ico/apple-touch-icon-114-precomposed.png">
  <link rel="apple-touch-icon-precomposed" sizes="72x72" href="../assets/ico/apple-touch-icon-72-precomposed.png">
                <link rel="apple-touch-icon-precomposed" href="../assets/ico/apple-touch-icon-57-precomposed.png">
                               <link rel="shortcut icon" href="../assets/ico/favicon.png">

<div class="navbar navbar-inverse navbar-fixed-top">
  <div class="navbar-inner">
    <div class="container">
      <button type="button" class="btn btn-navbar" data-toggle="collapse" data-target=".nav-collapse">
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="brand" href="#">Project name</a>
      <div class="nav-collapse collapse">
        <ul class="nav">
          <li class="active"><a href="#">Home</a></li>
          <li><a href="#about">About</a></li>
          <li><a href="#contact">Contact</a></li>
        </ul>
      </div><!--/.nav-collapse -->
    </div>
  </div>
</div>

<div class="container">

  <h1>Bootstrap starter template</h1>
  <p>Use this document as a way to quick start any new project.<br> All you get is this message and a barebones HTML document.</p>

</div> <!-- /container -->

<!-- Le javascript
================================================== -->
<!-- Placed at the end of the document so the pages load faster -->
<script src="../bootstrap/2.3.1/js/jquery.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-transition.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-alert.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-modal.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-dropdown.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-scrollspy.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-tab.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-tooltip.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-popover.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-button.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-collapse.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-carousel.js"></script>
<script src="../bootstrap/2.3.1/js/bootstrap-typeahead.js"></script>

我把换成3.3.7的CSS，头部logo就出错了。导航会变成这样。