Ive added my own css file in app/assets/stylesheets/application.css
registered the style with
config.register_stylesheet "application.css", :media => 'screen'
Works fine in development.
For production I did the following:
Rails.application.config.assets.precompile += %w( application.css )
config.assets.initialize_on_precompile = true
but Heroku still fails to serve the css file.