The only thing I've done here is:

1. Added node-sass to package.json and installed via npm

2. Rename app.component.css to app.component.scss so that is is sass instead of standard css

--Do not change the stylUrls ['app.component.css'] as the compiler will automatically compile the saas to css

3. Added class="demo" to the div I added in your app.component.html file so the div is styled as we are defining in app.component.scss .demo