navbar affix使navbar缩小

Question

我创建了一个导航栏，当我制作它时，它会缩小。我不知道为什么

  <!-- nav Bar   -->
 <nav class="navbar navbar-default ">
  <div class="container">
    <div class="navbar-header">
      <a class="navbar-brand" href="#">Nurse Page</a>
    </div>

      <ul class="nav navbar-nav navbar-right">
        <li class="dropdown"><a class="dropdown-toggle" data-toggle="dropdown" href="#">
    <i class="glyphicon glyphicon-user"></i>
    Nurse Name <span class="caret"></span></a>
      <ul class="dropdown-menu">
    <!--/. doctor options    -->

        <li><a href="#">Logout</a></li>

      </ul>
    </li>
      </ul>
    </div><!--/.nav-collapse -->
</nav>

我的导航栏代码