docs: add dark mode implementation plan

10-task plan covering CSS variables, preferences, FOUC prevention, reactive theme application, component updates, and testing. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
2026-10-12 20:06:57 +02:00 · 2026-03-21 08:47:20 +01:00
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+# Dark Mode Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add a dark parchment theme variant with system/light/dark toggle in Settings > Preferences.
+
+**Architecture:** CSS `[data-theme="dark"]` attribute on `<html>` overrides CSS variables in `app.css`. A blocking inline script in `app.html` prevents FOUC. Theme preference uses the existing `UserPreferences` key-value system. A reactive `isDarkMode` rune in `theme.svelte.ts` drives note card color switching.
+
+**Tech Stack:** SvelteKit, Svelte 5 runes, CSS custom properties, Tailwind CSS v4, Vitest, Playwright
+
+**Spec:** `docs/superpowers/specs/2026-03-20-dark-mode-design.md`
+
+---
+
+## File Map
+
+| Action | File | Responsibility |
+|--------|------|----------------|
+| Modify | `src/app.css` | Add `--grid-dot` to `:root`, add `[data-theme="dark"]` block, update `body::before` |
+| Modify | `src/app.html` | Add FOUC-prevention inline script |
+| Modify | `src/lib/types/preferences.ts` | Add `theme` field to `UserPreferences` |
+| Create | `src/lib/utils/theme.svelte.ts` | `applyTheme()`, reactive `isDarkMode` rune |
+| Modify | `src/lib/utils/colors.ts` | Add `NOTE_COLORS_DARK`, export `getNoteColor()` |
+| Modify | `src/routes/+layout.svelte` | Add theme `$effect` watcher |
+| Modify | `src/routes/(app)/settings/preferences/+page.svelte` | Add theme segmented toggle |
+| Modify | `src/lib/components/NoteCard.svelte` | Use `getNoteColor()` with `isDarkMode` |
+| Modify | `src/lib/components/NoteEditor.svelte` | Use `getNoteColor()` with `isDarkMode` |
+| Modify | `src/lib/components/ColorPicker.svelte` | Use dark color swatches when `isDarkMode` |
+| Skip | `src/routes/(share)/s/[token]/+page.svelte` | Out of scope per spec (public share pages) |
+| Modify | `.gitignore` | Add `.superpowers/` |
+| Create | `tests/unit/theme.test.ts` | Unit tests for `applyTheme` and `isDarkMode` |
+| Create | `tests/unit/colors.test.ts` | Unit tests for `getNoteColor` |
+| Create | `tests/e2e/dark-mode.spec.ts` | E2E tests for theme toggle, persistence, system detection |
+
+---
+
+### Task 1: CSS Dark Theme Variables
+
+**Files:**
+- Modify: `src/app.css:6-23` (`:root` block) and `src/app.css:36` (`body::before`)
+
+- [ ] **Step 1: Add `--grid-dot` to `:root` and add `[data-theme="dark"]` block**
+
+In `src/app.css`, add `--grid-dot: #1a1a2e;` to the end of the `:root` block, then add the dark theme block after `:root`:
+
+```css
+:root {
+	--bg-base: #f0e6d3;
+	--bg-surface: #faf5eb;
+	--primary: #C8860A;
+	--primary-hover: #E8A020;
+	--text: #1a1a2e;
+	--text-muted: #6b6272;
+	--border: #1a1a2e;
+	--border-subtle: #d4cabb;
+	--destructive: #a63d2f;
+	--error-bg: #f5e0db;
+	--error-border: #d4a69e;
+	--error-text: #8b2e1f;
+	--success-bg: #dce8d4;
+	--success-text: #3a5a2e;
+	--card-shadow: 2px 2px 0px var(--border-subtle);
+	--card-shadow-hover: 3px 3px 0px var(--primary);
+	--grid-dot: #1a1a2e;
+}
+
+[data-theme="dark"] {
+	--bg-base: #1a1715;
+	--bg-surface: #2a2520;
+	--text: #e8dcc8;
+	--text-muted: #9a8e7e;
+	--border: #e8dcc8;
+	--border-subtle: #3a3530;
+	--destructive: #d4604e;
+	--error-bg: #3a2020;
+	--error-border: #5a3030;
+	--error-text: #e8a090;
+	--success-bg: #203020;
+	--success-text: #90c880;
+	--card-shadow: 2px 2px 0px var(--border-subtle);
+	--card-shadow-hover: 3px 3px 0px var(--primary);
+	--grid-dot: #e8dcc8;
+}
+```
+
+- [ ] **Step 2: Update `body::before` to use `--grid-dot` variable**
+
+Replace the hardcoded color in the `body::before` rule:
+
+```css
+body::before {
+	content: '';
+	position: fixed;
+	inset: 0;
+	pointer-events: none;
+	opacity: 0.03;
+	background-image: repeating-conic-gradient(var(--grid-dot) 0% 25%, transparent 0% 50%);
+	background-size: 4px 4px;
+	z-index: 0;
+}
+```
+
+- [ ] **Step 3: Verify by temporarily adding `data-theme="dark"` to `app.html`**
+
+In `src/app.html`, temporarily change `<html lang="en">` to `<html lang="en" data-theme="dark">`. Run `make dev` and visually confirm dark background and light text. Then revert the change.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add src/app.css
+git commit -m "feat: add dark theme CSS variables and grid-dot extraction"
+```
+
+---
+
+### Task 2: Theme Preference Type
+
+**Files:**
+- Modify: `src/lib/types/preferences.ts`
+
+- [ ] **Step 1: Add `theme` field to `UserPreferences`**
+
+```typescript
+export interface UserPreferences {
+	theme: 'system' | 'light' | 'dark';
+	defaultNoteMode: 'richtext' | 'markdown';
+	defaultNoteColor: NoteColor;
+	hideFooter: boolean;
+	sidebarDefaultState: 'open' | 'collapsed';
+	notifyOnShare: boolean;
+	notifyOnCollabRemoved: boolean;
+	notifyOnNoteDeleted: boolean;
+}
+
+export const DEFAULT_PREFERENCES: UserPreferences = {
+	theme: 'system',
+	defaultNoteMode: 'richtext',
+	defaultNoteColor: 'default',
+	hideFooter: false,
+	sidebarDefaultState: 'open',
+	notifyOnShare: true,
+	notifyOnCollabRemoved: true,
+	notifyOnNoteDeleted: true
+};
+```
+
+Do NOT add `theme` to `BOOLEAN_PREF_KEYS`.
+
+- [ ] **Step 2: Commit**
+
+```bash
+git add src/lib/types/preferences.ts
+git commit -m "feat: add theme preference type (system/light/dark)"
+```
+
+---
+
+### Task 3: Theme Utility — `applyTheme` and `isDarkMode`
+
+**Files:**
+- Create: `src/lib/utils/theme.svelte.ts`
+- Test: `tests/unit/theme.test.ts`
+
+- [ ] **Step 1: Write failing tests for theme utility**
+
+Note: `theme.svelte.ts` uses module-scope `$state` which requires the Svelte compiler. The Vitest node environment does not process `.svelte.ts` runes correctly, so we test only the DOM side-effects of `applyTheme` (attribute and meta tag changes). The reactive `isDarkMode` / `getIsDarkMode()` behavior is covered by E2E tests instead.
+
+Create `tests/unit/theme.test.ts`:
+
+```typescript
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+
+// Mock $app/environment
+vi.mock('$app/environment', () => ({ browser: true }));
+
+describe('applyTheme', () => {
+	let applyTheme: (theme: 'system' | 'light' | 'dark') => void;
+
+	beforeEach(async () => {
+		// Reset DOM
+		document.documentElement.removeAttribute('data-theme');
+		const meta = document.querySelector('meta[name="theme-color"]');
+		if (meta) meta.remove();
+		const metaEl = document.createElement('meta');
+		metaEl.setAttribute('name', 'theme-color');
+		metaEl.setAttribute('content', '#f0e6d3');
+		document.head.appendChild(metaEl);
+
+		// Reset module state
+		vi.resetModules();
+		const mod = await import('$lib/utils/theme.svelte.js');
+		applyTheme = mod.applyTheme;
+	});
+
+	it('sets data-theme="dark" for dark mode', () => {
+		applyTheme('dark');
+		expect(document.documentElement.getAttribute('data-theme')).toBe('dark');
+	});
+
+	it('removes data-theme for light mode', () => {
+		document.documentElement.setAttribute('data-theme', 'dark');
+		applyTheme('light');
+		expect(document.documentElement.hasAttribute('data-theme')).toBe(false);
+	});
+
+	it('updates meta theme-color for dark mode', () => {
+		applyTheme('dark');
+		const meta = document.querySelector('meta[name="theme-color"]');
+		expect(meta?.getAttribute('content')).toBe('#1a1715');
+	});
+
+	it('updates meta theme-color for light mode', () => {
+		applyTheme('dark');
+		applyTheme('light');
+		const meta = document.querySelector('meta[name="theme-color"]');
+		expect(meta?.getAttribute('content')).toBe('#f0e6d3');
+	});
+
+	it('falls back to system for unknown values', () => {
+		// matchMedia returns false by default in jsdom → resolves to light
+		applyTheme('invalid' as 'system' | 'light' | 'dark');
+		expect(document.documentElement.hasAttribute('data-theme')).toBe(false);
+	});
+
+	it('resolves system preference to dark when prefers-color-scheme is dark', () => {
+		Object.defineProperty(window, 'matchMedia', {
+			writable: true,
+			value: vi.fn().mockImplementation((query: string) => ({
+				matches: query === '(prefers-color-scheme: dark)',
+				media: query,
+				addEventListener: vi.fn(),
+				removeEventListener: vi.fn(),
+				dispatchEvent: vi.fn()
+			}))
+		});
+		applyTheme('system');
+		expect(document.documentElement.getAttribute('data-theme')).toBe('dark');
+	});
+});
+```
+
+- [ ] **Step 2: Run tests to verify they fail**
+
+Run: `pnpm vitest run tests/unit/theme.test.ts`
+Expected: FAIL — module not found
+
+- [ ] **Step 3: Implement `theme.svelte.ts`**
+
+Create `src/lib/utils/theme.svelte.ts`:
+
+```typescript
+import { browser } from '$app/environment';
+
+const LIGHT_THEME_COLOR = '#f0e6d3';
+const DARK_THEME_COLOR = '#1a1715';
+
+let darkMode = $state(false);
+
+export function getIsDarkMode(): boolean {
+	return darkMode;
+}
+
+export function applyTheme(theme: 'system' | 'light' | 'dark'): void {
+	if (!browser) return;
+
+	// Validate input
+	if (theme !== 'system' && theme !== 'light' && theme !== 'dark') {
+		theme = 'system';
+	}
+
+	// Resolve system preference
+	let resolved = theme;
+	if (theme === 'system') {
+		resolved = window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
+	}
+
+	const isDark = resolved === 'dark';
+	darkMode = isDark;
+
+	if (isDark) {
+		document.documentElement.setAttribute('data-theme', 'dark');
+	} else {
+		document.documentElement.removeAttribute('data-theme');
+	}
+
+	const meta = document.querySelector('meta[name="theme-color"]');
+	if (meta) {
+		meta.setAttribute('content', isDark ? DARK_THEME_COLOR : LIGHT_THEME_COLOR);
+	}
+}
+```
+
+- [ ] **Step 4: Run tests to verify they pass**
+
+Run: `pnpm vitest run tests/unit/theme.test.ts`
+Expected: All PASS
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/lib/utils/theme.svelte.ts tests/unit/theme.test.ts
+git commit -m "feat: add theme utility with applyTheme and isDarkMode"
+```
+
+---
+
+### Task 4: Note Card Dark Colors
+
+**Files:**
+- Modify: `src/lib/utils/colors.ts`
+- Test: `tests/unit/colors.test.ts`
+
+- [ ] **Step 1: Write failing tests for `getNoteColor`**
+
+Create `tests/unit/colors.test.ts`:
+
+```typescript
+import { describe, it, expect } from 'vitest';
+import { getNoteColor, NOTE_COLORS, NOTE_COLORS_DARK } from '$lib/utils/colors.js';
+
+describe('getNoteColor', () => {
+	it('returns light color when isDark is false', () => {
+		expect(getNoteColor('default', false)).toBe('#faf5eb');
+		expect(getNoteColor('coral', false)).toBe('#faafa8');
+	});
+
+	it('returns dark color when isDark is true', () => {
+		expect(getNoteColor('default', true)).toBe('#2a2520');
+		expect(getNoteColor('coral', true)).toBe('#4a2522');
+	});
+
+	it('returns default color for unknown color name', () => {
+		expect(getNoteColor('unknown' as any, false)).toBe('#faf5eb');
+		expect(getNoteColor('unknown' as any, true)).toBe('#2a2520');
+	});
+
+	it('has matching keys in light and dark color maps', () => {
+		const lightKeys = Object.keys(NOTE_COLORS).sort();
+		const darkKeys = Object.keys(NOTE_COLORS_DARK).sort();
+		expect(lightKeys).toEqual(darkKeys);
+	});
+});
+```
+
+- [ ] **Step 2: Run tests to verify they fail**
+
+Run: `pnpm vitest run tests/unit/colors.test.ts`
+Expected: FAIL — `getNoteColor` and `NOTE_COLORS_DARK` not found
+
+- [ ] **Step 3: Add dark colors and helper to `colors.ts`**
+
+Update `src/lib/utils/colors.ts`:
+
+```typescript
+import type { NoteColor } from '$lib/types/index.js';
+
+export const NOTE_COLORS: Record<NoteColor, { bg: string; label: string }> = {
+	default: { bg: '#faf5eb', label: 'Default' },
+	coral: { bg: '#faafa8', label: 'Coral' },
+	peach: { bg: '#f39f76', label: 'Peach' },
+	sand: { bg: '#fff8b8', label: 'Sand' },
+	mint: { bg: '#e2f6d3', label: 'Mint' },
+	sage: { bg: '#b4ddd3', label: 'Sage' },
+	fog: { bg: '#d4e4ed', label: 'Fog' },
+	storm: { bg: '#aeccdc', label: 'Storm' },
+	dusk: { bg: '#d3bfdb', label: 'Dusk' },
+	blossom: { bg: '#f6e2dd', label: 'Blossom' },
+	clay: { bg: '#e9e3d4', label: 'Clay' },
+	chalk: { bg: '#efeff1', label: 'Chalk' }
+};
+
+export const NOTE_COLORS_DARK: Record<NoteColor, { bg: string; label: string }> = {
+	default: { bg: '#2a2520', label: 'Default' },
+	coral: { bg: '#4a2522', label: 'Coral' },
+	peach: { bg: '#4a3020', label: 'Peach' },
+	sand: { bg: '#3a3520', label: 'Sand' },
+	mint: { bg: '#2a3a22', label: 'Mint' },
+	sage: { bg: '#223a32', label: 'Sage' },
+	fog: { bg: '#222e3a', label: 'Fog' },
+	storm: { bg: '#1e2a35', label: 'Storm' },
+	dusk: { bg: '#352540', label: 'Dusk' },
+	blossom: { bg: '#3a2830', label: 'Blossom' },
+	clay: { bg: '#302e28', label: 'Clay' },
+	chalk: { bg: '#2e2e30', label: 'Chalk' }
+};
+
+export function getNoteColor(color: NoteColor, isDark: boolean): string {
+	const map = isDark ? NOTE_COLORS_DARK : NOTE_COLORS;
+	return (map[color] ?? map.default).bg;
+}
+
+export const COLOR_OPTIONS = Object.entries(NOTE_COLORS).map(([value, { label }]) => ({
+	value: value as NoteColor,
+	label
+}));
+```
+
+- [ ] **Step 4: Run tests to verify they pass**
+
+Run: `pnpm vitest run tests/unit/colors.test.ts`
+Expected: All PASS
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/lib/utils/colors.ts tests/unit/colors.test.ts
+git commit -m "feat: add dark note card colors and getNoteColor helper"
+```
+
+---
+
+### Task 5: FOUC Prevention Script
+
+**Files:**
+- Modify: `src/app.html`
+
+- [ ] **Step 1: Add inline script to `app.html`**
+
+Insert after the `<meta name="theme-color">` tag (line 6) and before `%sveltekit.head%` (line 15):
+
+```html
+    <script>
+      (function() {
+        try {
+          var p = JSON.parse(localStorage.getItem('crumbs-preferences') || '{}');
+          var t = p.theme || 'system';
+          if (t !== 'light' && t !== 'dark') t = 'system';
+          if (t === 'system') t = matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
+          if (t === 'dark') {
+            document.documentElement.setAttribute('data-theme', 'dark');
+            var m = document.querySelector('meta[name="theme-color"]');
+            if (m) m.content = '#1a1715';
+          }
+        } catch(e) {}
+      })();
+    </script>
+```
+
+- [ ] **Step 2: Commit**
+
+```bash
+git add src/app.html
+git commit -m "feat: add FOUC-prevention script for dark mode"
+```
+
+---
+
+### Task 6: Reactive Theme in Root Layout
+
+**Files:**
+- Modify: `src/routes/+layout.svelte`
+
+- [ ] **Step 1: Add theme `$effect` to root layout**
+
+The root layout currently imports CSS and registers the PWA service worker. Add the theme `$effect` here so both `(app)` and `(auth)` layouts get the theme applied. **Important:** Keep `initPreferences()` in `(app)/+layout.svelte` — do NOT move it here. The `(app)` layout reads `sidebarDefaultState` immediately after init, and moving init to the root layout would create a race condition. The root layout only watches the preference reactively via `$effect`, which fires after preferences are loaded.
+
+On auth pages (login/setup), `initPreferences()` hasn't been called, so `prefs.theme` will be `'system'` (the default). The FOUC script already handles the initial theme from localStorage, and the `$effect` will apply the correct theme once it runs.
+
+```svelte
+<script lang="ts">
+	import '../app.css';
+	import { onMount, onDestroy } from 'svelte';
+	import { pwaInfo } from 'virtual:pwa-info';
+	import { browser } from '$app/environment';
+	import { getPreferences } from '$lib/stores/preferences.svelte.js';
+	import { applyTheme } from '$lib/utils/theme.svelte.js';
+
+	let { children } = $props();
+	let mediaQuery: MediaQueryList | undefined;
+	let systemListener: ((e: MediaQueryListEvent) => void) | undefined;
+
+	const prefs = $derived(getPreferences());
+
+	onMount(async () => {
+		if (pwaInfo) {
+			const { registerSW } = await import('virtual:pwa-register');
+			registerSW({
+				immediate: true,
+				onRegistered(r: ServiceWorkerRegistration | undefined) {
+					console.log('SW Registered:', r);
+				},
+				onRegisterError(error: Error) {
+					console.log('SW registration error', error);
+				}
+			});
+		}
+	});
+
+	$effect(() => {
+		if (!browser) return;
+		const theme = prefs.theme ?? 'system';
+		applyTheme(theme);
+
+		// Listen for system preference changes when in system mode
+		if (systemListener && mediaQuery) {
+			mediaQuery.removeEventListener('change', systemListener);
+		}
+		if (theme === 'system') {
+			mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
+			systemListener = () => applyTheme('system');
+			mediaQuery.addEventListener('change', systemListener);
+		}
+	});
+
+	onDestroy(() => {
+		if (systemListener && mediaQuery) {
+			mediaQuery.removeEventListener('change', systemListener);
+		}
+	});
+
+	const webManifest = $derived(pwaInfo ? pwaInfo.webManifest.linkTag : '');
+</script>
+
+<svelte:head>
+	{@html webManifest}
+</svelte:head>
+
+{@render children()}
+```
+
+**Note:** `initPreferences()` stays in `(app)/+layout.svelte`. The root layout only adds the theme `$effect` and does not call `initPreferences()`.
+
+- [ ] **Step 2: Verify dev server works**
+
+Run `make dev`, open the app, go to Settings > Preferences. The theme toggle doesn't exist yet, but the app should render without errors. Check browser console for any issues.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add src/routes/+layout.svelte src/routes/\(app\)/+layout.svelte
+git commit -m "feat: add reactive theme watcher in root layout"
+```
+
+---
+
+### Task 7: Theme Toggle in Settings
+
+**Files:**
+- Modify: `src/routes/(app)/settings/preferences/+page.svelte`
+
+- [ ] **Step 1: Add theme segmented toggle**
+
+Add as the first preference section (before "Default note mode"):
+
+```svelte
+<!-- Theme -->
+<div class="space-y-2">
+	<span class="block text-sm font-medium text-[var(--text)]">Theme</span>
+	<div class="flex gap-1" role="group" aria-label="Theme">
+		{#each [['system', 'System'], ['light', 'Light'], ['dark', 'Dark']] as [value, label]}
+			<button
+				onclick={() => updatePreference('theme', value)}
+				class="rounded-sm border px-4 py-2 text-sm transition-colors {prefs.theme === value ? 'border-[var(--primary)] bg-[var(--primary)]/15 text-[var(--primary)] font-medium' : 'border-[var(--border-subtle)] text-[var(--text)] hover:border-[var(--primary)]'}"
+				data-testid="pref-theme-{value}"
+			>
+				{label}
+			</button>
+		{/each}
+	</div>
+</div>
+```
+
+- [ ] **Step 2: Manually test**
+
+Run `make dev`. Go to Settings > Preferences. Click System / Light / Dark and confirm:
+- Clicking "Dark" immediately applies dark theme
+- Clicking "Light" reverts to light theme
+- Clicking "System" follows OS preference
+- Refreshing the page persists the choice (no FOUC)
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add src/routes/\(app\)/settings/preferences/+page.svelte
+git commit -m "feat: add theme toggle to preferences settings"
+```
+
+---
+
+### Task 8: Update Components to Use Dark Note Colors
+
+**Files:**
+- Modify: `src/lib/components/NoteCard.svelte:2,29-32`
+- Modify: `src/lib/components/NoteEditor.svelte:12,194-197`
+- Modify: `src/lib/components/ColorPicker.svelte`
+
+**Important:** `getIsDarkMode()` must be called **inside** `$effect` or `$derived` blocks for reactivity. Calling it as a top-level `const` would capture the value once and never update when the theme changes. Each component already has an `$effect` block where it computes card/bg styles — add `getIsDarkMode()` inside those existing blocks.
+
+Public share page (`src/routes/(share)/s/[token]/+page.svelte`) is out of scope per the spec.
+
+- [ ] **Step 1: Update `NoteCard.svelte`**
+
+Replace `NOTE_COLORS` import with `getNoteColor` and `getIsDarkMode`:
+
+```svelte
+<!-- Change import at top of script -->
+import { getNoteColor } from '$lib/utils/colors.js';
+import { getIsDarkMode } from '$lib/utils/theme.svelte.js';
+
+<!-- Inside the existing $effect block where cardStyle is computed (around lines 29-32): -->
+$effect(() => {
+	// ... existing logic ...
+	const bg = getNoteColor(note.color, getIsDarkMode());
+	cardStyle = `background-color: ${bg}`;
+});
+```
+
+Remove the `NOTE_COLORS` import. `getIsDarkMode()` is called inside the `$effect` so it re-runs when the theme changes.
+
+- [ ] **Step 2: Update `NoteEditor.svelte`**
+
+Same pattern — inside the existing `$effect` where `bgStyle` is computed:
+
+```svelte
+import { getNoteColor } from '$lib/utils/colors.js';
+import { getIsDarkMode } from '$lib/utils/theme.svelte.js';
+
+<!-- Inside the existing $effect (around lines 194-197): -->
+bgStyle = `background-color: ${getNoteColor(color, getIsDarkMode())}`;
+```
+
+Remove the `NOTE_COLORS` import.
+
+- [ ] **Step 3: Update `ColorPicker.svelte`**
+
+The ColorPicker shows circular swatches. Use `$derived` for the dark mode check so swatches update reactively:
+
+```svelte
+import { COLOR_OPTIONS, getNoteColor } from '$lib/utils/colors.js';
+import { getIsDarkMode } from '$lib/utils/theme.svelte.js';
+
+<!-- Use getIsDarkMode() in the template directly (it's reactive in Svelte 5 template expressions): -->
+style="background-color: {getNoteColor(option.value, getIsDarkMode())}"
+```
+
+Remove `NOTE_COLORS` import if no longer needed.
+
+- [ ] **Step 4: Verify all components render correctly in both themes**
+
+Run `make dev`. Toggle between light and dark in Settings > Preferences. Check:
+- Note cards show correct dark/light background colors
+- Color picker shows dark/light swatches
+- Note editor uses correct background color
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/lib/components/NoteCard.svelte src/lib/components/NoteEditor.svelte src/lib/components/ColorPicker.svelte
+git commit -m "feat: use dark note card colors in all components"
+```
+
+---
+
+### Task 9: E2E Tests
+
+**Files:**
+- Create: `tests/e2e/dark-mode.spec.ts`
+
+- [ ] **Step 1: Write E2E tests**
+
+Create `tests/e2e/dark-mode.spec.ts`:
+
+```typescript
+import { test, expect } from './helpers/fixtures.js';
+
+test.describe('Dark mode', () => {
+	test('Scenario: Theme toggle persists selection across page reload', async ({
+		authenticatedPage: page
+	}) => {
+		// Given the user is on the preferences page
+		await page.goto('/settings/preferences');
+
+		// When the user selects dark theme
+		await page.getByTestId('pref-theme-dark').click();
+
+		// Then the page applies dark theme
+		await expect(page.locator('html')).toHaveAttribute('data-theme', 'dark');
+
+		// When the page is reloaded
+		await page.reload();
+
+		// Then the dark theme persists without flash
+		await expect(page.locator('html')).toHaveAttribute('data-theme', 'dark');
+		await expect(page.getByTestId('pref-theme-dark')).toHaveClass(/font-medium/);
+	});
+
+	test('Scenario: Light mode removes dark theme attribute', async ({
+		authenticatedPage: page
+	}) => {
+		// Given dark theme is active
+		await page.goto('/settings/preferences');
+		await page.getByTestId('pref-theme-dark').click();
+		await expect(page.locator('html')).toHaveAttribute('data-theme', 'dark');
+
+		// When the user selects light theme
+		await page.getByTestId('pref-theme-light').click();
+
+		// Then the dark theme attribute is removed
+		await expect(page.locator('html')).not.toHaveAttribute('data-theme');
+	});
+
+	test('Scenario: System mode follows OS dark preference', async ({
+		authenticatedPage: page
+	}) => {
+		// Given the OS prefers dark mode
+		await page.emulateMedia({ colorScheme: 'dark' });
+
+		// When the user selects system theme
+		await page.goto('/settings/preferences');
+		await page.getByTestId('pref-theme-system').click();
+
+		// Then the page applies dark theme from system preference
+		// Use toHaveAttribute with timeout to handle async $effect execution
+		await expect(page.locator('html')).toHaveAttribute('data-theme', 'dark', { timeout: 5000 });
+	});
+
+	test('Scenario: Note cards use dark colors in dark mode', async ({
+		authenticatedPage: page
+	}) => {
+		// Given dark theme is active
+		await page.goto('/settings/preferences');
+		await page.getByTestId('pref-theme-dark').click();
+
+		// When viewing the notes page
+		await page.goto('/');
+
+		// Then note cards should have dark background colors
+		const noteCard = page.getByTestId('note-card').first();
+		if (await noteCard.isVisible()) {
+			const bg = await noteCard.evaluate((el) => getComputedStyle(el).backgroundColor);
+			// Dark default color is #2a2520 = rgb(42, 37, 32)
+			expect(bg).not.toBe('rgb(250, 245, 235)'); // Not the light default
+		}
+	});
+});
+```
+
+- [ ] **Step 2: Run E2E tests**
+
+Run: `pnpm test:e2e tests/e2e/dark-mode.spec.ts`
+Expected: All PASS
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add tests/e2e/dark-mode.spec.ts
+git commit -m "test: add E2E tests for dark mode toggle and persistence"
+```
+
+---
+
+### Task 10: Housekeeping and Type Check
+
+**Files:**
+- Modify: `.gitignore`
+
+- [ ] **Step 1: Add `.superpowers/` to `.gitignore`**
+
+Append to `.gitignore`:
+
+```
+# Superpowers brainstorm artifacts
+.superpowers/
+```
+
+- [ ] **Step 2: Run type check**
+
+Run: `pnpm check`
+Expected: No errors. If there are type errors, fix them.
+
+- [ ] **Step 3: Run full test suite**
+
+Run: `make test`
+Expected: All unit and E2E tests pass.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add .gitignore
+git commit -m "chore: add .superpowers/ to gitignore"
+```