I just found the amazing Stackblitz online VS Code editor. I created an Angular project and under dependencies installed the Bootstrap CSS framework but how
Check this StackBlitz example : https://stackblitz.com/edit/angular-wkc7ix?file=styles.css
It does have a angular-cli.json file and a style.css file
angular-cli.json :
{ "apps": [{ "styles": ["styles.css"] }] }
style.css :
@import "bootstrap/dist/css/bootstrap.min.css";