anchor.diff:            <li><%= link_to "登录", signin_path %></li>
           <% end %>
         </ul>
  -    </nav>
  +    </div>
     </div>
  -</header>+</nav>
positive.code:       </button>
        <a href="/" class="navbar-brand"><%=image_tag("mech-logo-s.png",:class => "mech-nav-logo")%></a>
      </div>
      <nav class="navbar-collapse collapse">
        <ul class="nav navbar-nav">
          <li>
            <a href="/">首页</a>
  
negative.code: <nav class="navbar navbar-inverse navbar-static-top mech-nav">
    <div class="container">
      <div class="navbar-header">
        <button class="navbar-toggle" type="button">
  