[CL-499][PM-14020] compact mode (#11796)

libs/components/src/shared/compact-mode.service.ts

@@ -0,0 +1,11 @@
+import { Observable } from "rxjs";
+
+/** Global config for the Bitwarden Design System */
+export abstract class CompactModeService {
+  /**
+   * When true, enables "compact mode".
+   *
+   * Component authors can also hook into compact mode with the `bit-compact:` Tailwind variant.
+   **/
+  enabled$: Observable<boolean>;
+}