def shadow
    content_tag :div, :class => 'b-shadow' do
      result = ''
      result += content_tag :div, '', :class => 'b-shadow-left'
      result += content_tag :div, '', :class => 'b-shadow-right'
      result += content_tag :div, '', :class => 'b-shadow-center'
      result.html_safe
    end
  end