Need help with instructions for NPM / webpack addition

This is my first NPM package I've ever written. 

I'd like to offer people an intuitive way to install the package using `npm install`, and it just works. 

However I couldn't work out how to add the CSS when everyone's path to node_modules will be different. 

At the moment, I'm cheating, by just loading the CDN version. See: index.js

Any help appreciated. 