Call it with <%= stylesheet_link_tag(*get_stylesheets) %> in your layouts file

application_helper.rb

def get_stylesheets
  styles_path = "#{Rails.root}/public/stylesheets"
  controller_name = controller.controller_path
  action_name = controller.action_name
  if File.exists? "#{styles_path}/#{controller_name}/#{action_name}.css"
    "#{controller_name}/#{action_name}"
  elsif ["create","edit","update"].include? action_name and File.exists? " #{styles_path}/#{controller_name}/new.css"
    "#{controller_name}/new"
  end
end