@@ -1030,7 +1030,11 @@ export class ApplicationCommon {
 			return;
 		}
 		this._systemAppearance = value;
-		this.systemAppearanceChanged(this.getRootView(), value);
+		// `autoSystemAppearanceChanged` opts out of the CSS classes only: the event
+		// still fires so apps driving their own theming can react to it.
+		if (this.autoSystemAppearanceChanged) {
+			this.systemAppearanceChanged(this.getRootView(), value);
+		}
 		this.notify(<SystemAppearanceChangedEventData>{
 			eventName: this.systemAppearanceChangedEvent,
 			android: this.android,
@@ -1055,12 +1059,15 @@ export class ApplicationCommon {
 	}
 
 	/**
-	 * Updates root view classes including those of modals
+	 * Updates root view classes including those of modals.
+	 * Applies them even when automatic updates are disabled with
+	 * `setAutoSystemAppearanceChanged(false)`, so an app can set its own
+	 * appearance.
 	 * @param rootView the root view
 	 * @param newSystemAppearance the new appearance change
 	 */
 	systemAppearanceChanged(rootView: View, newSystemAppearance: 'dark' | 'light'): void {
-		if (!rootView || !this.autoSystemAppearanceChanged) {
+		if (!rootView) {
 			return;
 		}
 
 
@@ -0,0 +1,143 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+
+// `application.android.ts` registers deferred event wiring while it loads, through a hook the
+// `NativeScriptGlobals` stub in `vitest.setup.ts` does not carry. Hoisted so it lands before
+// the imports below.
+vi.hoisted(() => {
+	(globalThis as any).NativeScriptGlobals.addEventWiring = () => {};
+});
+
+import { CoreTypes } from '../core-types';
+import { Observable } from '../data/observable';
+import type { View } from '../ui/core/view';
+import { ApplicationCommon } from './application-common';
+import { AndroidApplication } from './application.android';
+import { setNativeApp } from './helpers-common';
+
+/** See application-registry.spec.ts: makes the application's events observable. */
+function installApplicationEventBus(): Observable {
+	const events = new Observable();
+	const bus = (global.NativeScriptGlobals as any).events;
+
+	bus.on = events.on.bind(events);
+	bus.once = events.once.bind(events);
+	bus.off = events.off.bind(events);
+	bus.notify = events.notify.bind(events);
+	bus.hasListeners = events.hasListeners.bind(events);
+
+	return events;
+}
+
+function createRootView() {
+	return {
+		cssClasses: new Set<string>(),
+		_onCssStateChange: vi.fn(),
+		_getRootModalViews: () => [],
+	};
+}
+
+class TestApplication extends ApplicationCommon {
+	rootView = createRootView();
+
+	getRootView(): View {
+		return this.rootView as unknown as View;
+	}
+
+	getOrientation(): 'portrait' | 'landscape' | 'unknown' {
+		return 'portrait';
+	}
+
+	getSystemAppearance(): 'dark' | 'light' | null {
+		return 'light';
+	}
+
+	getLayoutDirection(): CoreTypes.LayoutDirectionType | null {
+		return CoreTypes.LayoutDirection.ltr;
+	}
+
+	changeSystemAppearance(value: 'dark' | 'light') {
+		this.setSystemAppearance(value);
+	}
+}
+
+describe('system appearance', () => {
+	let app: TestApplication;
+
+	beforeEach(() => {
+		installApplicationEventBus();
+		app = new TestApplication();
+	});
+
+	afterEach(() => {
+		app.setAutoSystemAppearanceChanged(true);
+		installApplicationEventBus();
+	});
+
+	it('applies the appearance an app sets while automatic changes are off', () => {
+		app.setAutoSystemAppearanceChanged(false);
+
+		app.systemAppearanceChanged(app.getRootView(), 'dark');
+
+		expect(app.rootView.cssClasses.has('ns-dark')).toBe(true);
+		expect(app.rootView._onCssStateChange).toHaveBeenCalled();
+	});
+
+	it('leaves the classes alone when the system changes while automatic changes are off', () => {
+		const changes: string[] = [];
+		app.on(app.systemAppearanceChangedEvent, (args: any) => changes.push(args.newValue));
+		app.setAutoSystemAppearanceChanged(false);
+
+		app.changeSystemAppearance('dark');
+
+		expect(app.rootView.cssClasses.has('ns-dark')).toBe(false);
+		expect(changes).toEqual(['dark']);
+	});
+
+	it('applies system changes while automatic changes are on', () => {
+		app.changeSystemAppearance('dark');
+
+		expect(app.rootView.cssClasses.has('ns-dark')).toBe(true);
+	});
+});
+
+describe('Android application traits before the app has started', () => {
+	const UI_MODE_NIGHT_YES = 0x20;
+	let globals: Record<string, any>;
+
+	beforeEach(() => {
+		installApplicationEventBus();
+		globals = { android: (global as any).android };
+		(global as any).android = {
+			...globals.android,
+			content: {
+				...globals.android?.content,
+				res: {
+					Configuration: {
+						UI_MODE_NIGHT_MASK: 0x30,
+						UI_MODE_NIGHT_UNDEFINED: 0x00,
+						UI_MODE_NIGHT_NO: 0x10,
+						UI_MODE_NIGHT_YES,
+						ORIENTATION_PORTRAIT: 1,
+						ORIENTATION_LANDSCAPE: 2,
+					},
+				},
+			},
+		};
+		const configuration = { uiMode: 0x01 | UI_MODE_NIGHT_YES, orientation: 2 };
+		setNativeApp({ getResources: () => ({ getConfiguration: () => configuration }) } as any);
+	});
+
+	afterEach(() => {
+		(global as any).android = globals.android;
+		setNativeApp(undefined);
+		installApplicationEventBus();
+	});
+
+	it('reads them from the native application', () => {
+		const app = new AndroidApplication();
+
+		expect(app.context).toBeUndefined();
+		expect(app.systemAppearance()).toBe('dark');
+		expect(app.orientation()).toBe('landscape');
+	});
+});