I use rails and bootstrap by using this bootstrap-sass
I've moved
application.css
application.scss
*= require_tree
assets/stylesheets
@import "freelancer";
@import "freelancer.css";
@import "freelancer.css"!force;
Scss being a superset of css, you can just change your .css extension to .scss, it will still work in the same way.
Then you can require them like this, and it should work:
@import "freelancer";