Require statement doesn't work in application.css

I've been using the bootstrap theme as a link from my application.html.erb, but I've recently instaled the gem "twitter-bootstrap-rails". I got the javascript part of the gem working, but I still have to use the link for css. Requiring bootstrap in application.css doesn't work.

applicatio.css

*= require bootstrap *= require bootstrap-datetimepicker

I'm posting because all of the links that I could find use application.css.scss