Now, you could do as they suggest and load specific stylesheets for each controller, but it does not work as they suggest out of the box. The neglect to mention a few things you must do.
You need to remove the //= require_tree . directive from application.css, which, left in place, will load every other asset in the folder. This means that every page would load users.css, and if you added the controller-specific stylesheet line as in their example, it would load the controller stylesheet twice.
You would need to tell Rails to precompile the individual files. By default, all *.css files besides application.css are ignored by the precompiler. To fix this you'd have to do edit your config to do something like this:
# in environments/production.rb
# either render all individual css files:
config.assets.precompile << "*.css"
# or include them individually
config.assets.precompile += %w( users.css static_pages.css )
Finally, as instructed by the Rails guide, you'd need to change your stylesheet includes to look something like:
<%# this would now only load application.css, not the whole tree %>
<%= stylesheet_link_tag :application, :media => "all" %>
<%# and this would load the controller specific file %>
<%= stylesheet_link_tag params[:controller] %>
However, the above may not be truly the best practice. Sure, sometimes you might want individual stylesheets, but most the time you probably just want to serve your style bundle so the client can cache one file. This is how the asset pipeline works out of the box, after all.
Besides that, if you were to just add override rules in your controller specific stylesheets, then you're creating a load-order-specific tangle of styles right out of the gate. This... is probably not good.
A better approach might be to namespace the styles in the controller sheets, something like this:
// in application.css (or some other commonly loaded file)
// in users.css.scss
// and so on...
Then in your layout, add the controller name to the body class, like:
<body class="controller-<%= params[:controller] %>">
In this way, your styles are resolved by namespace, not just load order. Furthermore with this solution you could still go ahead and load separate controller-specific stylesheets if you desire, or you could forget about that and just let everything be compiled into application.css as it would be by default. All the styles would be loaded for each page, but only the controller-specific styles would apply.
This is a great answer, all the more because it takes a good practice, commonly shared in this community, it shows its downsides and it proposes a much better alternative. Many thanks!!