Angular 2+ theme button colors not working

I have a stackblitz example here that I believe is set up following the Angular theming documentation, and yet the colors in the following code are not displaying:

<button mat-raised-button color="primary">Primary</button>
<button mat-raised-button color="accent">Accent</button>
<button mat-raised-button color="warn">Warn</button>
<button mat-raised-button disabled>Disabled</button>

What's more, I'm brand new to stackblitz and can't find where the body tag is (it's not in index.html?!), so I assigned the my-app tag the class,"mat-app-background":

<my-app class="mat-app-background">loading</my-app>

I have looked through several SO entries (e.g. this)and github issues pages (e.g., this), and none seem to be relevant to my issue or current. Any help is much appreciated.

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