css foler design.rb

# app/views/layouts/application.html.erb

<%= render_stylesheets content_for(:stylesheets) %>

# app/helpers/layout_helper.rb
  def render_stylesheets(tag_html = nil)
    html = []
    if tag_html.present?
      html << tag_html
    else
      html << stylesheet_link_tag('application', :media => 'all')
      html << stylesheet_link_tag(namespace, :media => 'all')
    end
    html.join("\n").html_safe
  end
  
  def namespace
    controller_path.split('/').first
  end
  
  
# for special need
<% content_for :stylesheets do %>
<%= stylesheet_link_tag 'application' %>
<%= stylesheet_link_tag 'contact_recordings' %>
<% end %>