docs(aio): fix paths to imported CSS stylesheets (#21772)

The AOT compiler needs relative paths so that it can find
the imported stylesheets.

PR Close #21772

aio/content/examples/component-styles/src/app/hero-details.component.css

@@ -1,5 +1,6 @@
 /* #docregion import */
-@import 'hero-details-box.css';
+/* The AOT compiler needs the `./` to show that this is local */
+@import './hero-details-box.css';
 /* #enddocregion import */
 
 /* #docregion host */

aio/content/examples/component-styles/src/app/hero-team.component.ts

@@ -5,7 +5,8 @@ import { Hero } from './hero';
 @Component({
   selector: 'app-hero-team',
   template: `
-    <link rel="stylesheet" href="assets/hero-team.component.css">
+    <!-- We must use a relative URL so that the AOT compiler can find the stylesheet -->
+    <link rel="stylesheet" href="../assets/hero-team.component.css">
     <h3>Team</h3>
     <ul>
       <li *ngFor="let member of hero.team">