How do I use CSS with a ruby on rails application?

Use the rails style sheet tag to link your main.css like this

<%= stylesheet_link_tag "main" %>

Go to

config/initializers/assets.rb

Once inside the assets.rb add the following code snippet just below the Rails.application.config.assets.version = '1.0'

Rails.application.config.assets.version = '1.0'
Rails.application.config.assets.precompile += %w( main.css )

Restart your server.

If you are using rails > 3 version, then there is a concept called asset pipeline. You could add your CSS to

app/assets/stylesheets

then it will automatically be picked up by the app. (this is useful as rails will automatically compress the CSS files)

read more here about the asset pipeline

Put the CSS files in public/stylesheets and then use:

<%= stylesheet_link_tag "filename" %>

to link to the stylesheet in your layouts or erb files in your views.

Similarly you put images in public/images and javascript files in public/javascripts.

I did the following...

1. place your css file in the app/assets/stylesheets folder.
2. Add the stylesheet link <%= stylesheet_link_tag "filename" %> in your default layouts file (most likely application.html.erb)

I recommend this over using your public folder. You can also reference the stylesheet inline, such as in your index page.