tap/app/views/layouts/_header.html.erb

<nav class="navbar navbar-inverse navbar-fixed-top" role="navigation">
  <div class="container-fluid">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <%= link_to "Taþ", root_path, class: "navbar-brand" %>
    </div>

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <div class="hidden-xs navbar-form navbar-right">
        <div class="form-group">
        <% if user_signed_in? %>
          <%= button_to "Logout", destroy_user_session_path(current_user), class: "btn btn-default form-control",  method: :delete %>
        <% else %>
          <%= button_to "Login", new_user_session_path, class: "btn btn-success form-control" %>
        <% end %>
        </div>
      </div>

      <ul class="nav navbar-nav navbar-right">
        <li><%= mail_to "tab@zeus.ugent.be", "Send feedback" %></li>
        <% if can? :manage, :all %>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">Products <span class="caret"></span></a>
          <ul class="dropdown-menu" role="menu">
            <li><%= link_to "All products", products_path %></li>
            <li><%= link_to "New product" , new_product_path %></li>
          </ul>
        </li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">Users <span class="caret"></span></a>
          <ul class="dropdown-menu" role="menu">
            <li><%= link_to "index" , users_path %></li>
          </ul>
        </li>
        <% end %>
        <% if user_signed_in? %>
        <li>
          <a>Logged in as <%= current_user.display_name %></a>
        </li>
        <% end %>
      </ul>

      <div class="visible-xs navbar-form">
        <div class="form-group">
        <% if user_signed_in? %>
          <%= button_to "Logout", destroy_user_session_path(current_user), class: "btn btn-default form-control",  method: :delete %>
        <% else %>
          <%= button_to "Login", new_user_session_path, class: "btn btn-success form-control" %>
        <% end %>
        </div>
      </div>

    </div><!-- /.navbar-collapse -->
  </div><!-- /.container-fluid -->
</nav>