Setting styles to angular components in angular.component.html by using divs

I’m new to angular coding and I am following the course on angular4.

The problem I’m having is that everytime I want to style an component in app.component.html I have to wrap that component in a div to make the styles in the app.component.css to apply.

Is that really the only way to make it work? There has to be other ways…
I have searched the internet but cannot find a good answer to this.

regards/ aj