controller_name/action_name.js (e.g. home.js, customers.js, etc.); and
controller_name/action_name.js (eg. home/index.js, customers/new.js, etc.).
You have two choices for installation. The first uses a gem (recommended):
Or you can use the Rails plugin
Cascading Stylesheets: github.com/harukizaemon/cascading_stylesheets
This plugin is copyright 2009 by Simon Harris and is released under the MIT license.