UnCSS not able to find stylesheet in backbone appl

Question

So my application is much in need of a CSS clean up. I did some research and I came across uncss, which seems like the best option out there so far.

A little about my application:

• It's a backbone.marionette app
• I use Sass
• I compile all my assets into public/js/app.js and public/css/main.css using the amazing tool brunch.io

I've tried running both the command line tool offered in uncss, and the brunch extension of uncss. But each time I run the process, I get this error:

Error: UnCSS: no stylesheets found

Also, if anyone has any experience with brunch, this is how I add the rule to my config.coffee:

uncss:
  options:
    csspath: 'css/main.css'
    htmlroot: 'public'
  files: ['index.html']

Anyone come across this error? Does it have anything to do with the fact that I'm using a framework like backbone.marionette?