1. Set Schematics

By default Angular CLI will use .css styles extension when generating new components. To convert to .scss run the following line:

ng config schematics.@schematics/angular:component.style scss

Open angular.json and in schematics you will see the following line:

"style": "scss",

NB: Any existing .css files will need to be converted manually.

Next

Sass Architecture

Reference

Sass