Multiple custom CSS for Formtastic

Inside stylesheets I have formtastic.css and formtastic_changes.css. In formtastic_changes.css I have a custom with:

form.formtastic { width: 700px; etc..

It is working ok but now in only one page only, need a narrower form, say 530. So I need to have two width set up.

What is the best way to do this? I mean I do not want to change the other forms in the project, I just want to change the width of only one new form.

Thank you

There are other classes added to the form that may be appropriate to use as a hook (eg "post"), and you can also add your own classes to the form using the same :html option in Rails' form_for helper.