Angular can't resolve relative path of app.component.html. Just replace ./app.component.html with src/app.component.html and you are good to go.
Here is what the above code is Doing:
1. The @Component decorator is a function that takes a metadata object as argument.
2. The metadata object has a selector property that tells Angular to display the component inside a custom HTML tag called app-root.
3. The metadata object has a templateUrl property that tells Angular to display the component’s view inside the app-root tag.
4. The metadata object has a styleUrls property that tells Angular to apply the component’s styles to the app-root tag.