How do I set the HTML options for collection_select in Rails?

I can't seem to find the syntax to add a class to a select tag generated by Rails collection_select. Some help?

Many Rails helpers take multiple hash arguments. The first is usually the options to control the helper itself, and the second is the html_options where you specifiy custom ids, classes etc.

The method definition looks like this:

collection_select(object, method, collection, value_method, text_method, options = {}, html_options = {})

You'll notice the multiple '= {}' in the params list. To use this, the first set of options that you would specify must actually be enclosed in braces:

collection_select(:user, :title, UserTitle.all, :id, :name, {:prompt=>true}, {:class=>'my-custom-class'})

If you don't have any options to specify besides the html class, then just put an empty hash placeholder:

collection_select(:user, :title, UserTitle.all, :id, :name, {}, {:class=>'my-custom-class'})

Additional API documentation is available at: http://apidock.com/rails/ActionView/Helpers/FormOptionsHelper/collection_select

= f.collection_select :category_id, Category.order(:name), :id, :name, {}, {class: "store-select"}