ruby on rails - Search field and box in Nav bar using zurb has black background -

i ran weird bug ruby on rails app want display search field , button in navbar view looks image

the problem has black in background search box , button.

the following code below:

<section class="top-bar-section">    <ul class="left">      <%= form_tag('/search') %>        <li>          <%= text_field_tag :query, nil ,:placeholder => "search designs", :id=>"nav_search_box" %>        </li>        <li>          <%= submit_tag 'search', :class=>"round button", :id=>"nav_search_btn" %>        </li>      <% end %>    </ul>  </section> 

any insight on fixing bug appreciated!

this explained in official docs, under other elements.

http://foundation.zurb.com/docs/components/top-bar.html

"can use small foundation button in nav, include has-form class parent li."