adding css file explicitly to PHP MVC project for class/ID autocompletion

As per MVC, the main project css file is loaded in the wrapper layout file, which is rendered before each view.

My goal is that when I'm working on a view, ideally, I'd like to have bootstrap and other css selectors in my project be autocompleted.

Any css explicitly in the view file of course works fine, but it doesn't know to look in my main project CSS file.  Would you please try to help me where to add it in the project so that autocomplete will know about it? It's in the project structure, it's included when the layout is rendered...

FWIW, I'm using the Yii MVC framework with the Framework MVC Structure Support plugin

PS, this is the best editor I've used ever and that's saying a lot. Amazing work.  Just some things like this, escape me.  Thank you for your time.

IntelliJ IDEA Ultimate 2016.3