diff --git a/frontend/e2e/theme.spec.ts b/frontend/e2e/theme.spec.ts
index 037b9fcf..168f4fcf 100644
--- a/frontend/e2e/theme.spec.ts
+++ b/frontend/e2e/theme.spec.ts
@@ -60,6 +60,20 @@ test.describe('Theme toggle', () => {
 		await expect(page.locator('html')).toHaveAttribute('data-theme', 'dark');
 	});
 
+	test('header uses --c-header token background in dark mode', async ({ page }) => {
+		await page.goto('/');
+		await page.waitForSelector('[data-hydrated]');
+
+		await page.evaluate(() => document.documentElement.setAttribute('data-theme', 'dark'));
+
+		const headerBg = await page.evaluate(() => {
+			const header = document.querySelector('header');
+			return header ? getComputedStyle(header).backgroundColor : null;
+		});
+		// --c-header in dark mode = #01335e → rgb(1, 51, 94)
+		expect(headerBg).toBe('rgb(1, 51, 94)');
+	});
+
 	test('color-scheme is dark when data-theme=dark is set', async ({ page }) => {
 		await page.goto('/');
 		await page.waitForSelector('[data-hydrated]');