angular-cli/docs/documentation/stories/css-preprocessors.md

CSS Preprocessor integration

Angular CLI supports all major CSS preprocessors:

• sass/scss (http://sass-lang.com/)
• less (http://lesscss.org/)
• stylus (http://stylus-lang.com/)

To use these preprocessors simply add the file to your component's styleUrls:

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent {
  title = 'app works!';
}

When generating a new project you can also define which extension you want for style files:

ng new sassy-project --style=sass

Or set the default style on an existing project:

ng set defaults.styleExt scss