Product Requirements Document (PRD): Dark Theme for Memory Game
1. Overview
Product
Memory Game
Objective
Add a dark theme option to the existing memory game so the interface is more comfortable in low-light conditions and provides a modern, polished visual experience.
Problem Statement
The current game uses a light color palette. While it works well in daylight, it can feel visually harsh in dim environments and may not match user preferences for dark interfaces. A dark theme improves usability, reduces eye strain, and creates a more premium experience.
Goal
Introduce a toggleable dark theme that preserves all current gameplay behavior and improves readability, accessibility, and visual consistency.
2. Background and Context
The project is a simple browser-based memory card game built with HTML, CSS, and JavaScript. It already contains gameplay features such as:
- card matching logic
- move counter
- timer
- star rating
- grid size selection
- best score storage
This project is a lightweight front-end exercise and the dark theme feature should be implemented without altering the game’s core logic or structure.
3. Users
Primary Users
- Players using the game in low-light conditions
- Users who prefer darker interfaces
- Casual browser game users
Secondary Users
- Accessibility-conscious users
- Developers reviewing and learning front-end UI patterns
4. Product Goals
- Allow users to switch between light and dark themes.
- Maintain readability, usability, and accessibility in both themes.
- Keep the feature lightweight and easy to maintain.
- Preserve the current game experience without breaking gameplay.
- Persist the user’s theme preference across refreshes.
5. Scope
In Scope
- Dark mode for the full game interface
- Theme toggle button
- Improved color contrast and accessibility
- Theme persistence via browser storage
- Support for keyboard-friendly interaction
Out of Scope
- Multiple theme packs beyond light and dark
- Sound effects or background music
- Game mechanic redesign
- New multiplayer functionality
6. User Stories
- As a player, I want to switch to dark mode so I can play comfortably at night.
- As a player, I want the board, controls, and modal to match the selected theme so the app feels consistent.
- As a player, I want my selected theme to remain saved after refreshing the page.
- As a player, I want text and buttons to remain readable in dark mode.
- As a developer, I want the theme implementation to be maintainable and not interfere with game logic.
7. Functional Requirements
7.1 Theme Toggle
The game must provide a visible toggle control to switch between light and dark modes.
7.2 Theme States
The game must support:
- light theme (default)
- dark theme
7.3 Layout and Visual Updates
When the user toggles themes:
- page background color changes
- card colors change appropriately
- panel, stat, and modal colors update
- text remains readable and visually balanced
- button hover and active states still work correctly
7.4 Persistence
The selected theme should persist using localStorage so it remains after reload.
7.5 Accessibility
- Focus outlines must remain visible in dark mode
- Text contrast should remain high enough for readability
- Theme toggle must be keyboard accessible
8. Non-Functional Requirements
- Theme switching should feel instant
- No visible lag or usability issues when toggling
Maintainability
- Theme values should be centralized using CSS variables or a consistent theming structure
- Styling should be easy to extend for future themes
Accessibility
- Contrast must be suitable for normal reading and interaction
- The toggle should be usable by keyboard and screen readers
9. UI/UX Requirements
Recommended Theme Palette
- Background: dark navy / charcoal
- Panels: dark gray or slate
- Card back: blue or deep accent
- Card front: dark surface with light text
- Primary buttons: blue / cyan accent tones
- Text: near-white or light gray
- Success / rating indicators: preserve strong visibility
Interaction Design
- Theme changes should transition smoothly
- The layout should not shift unexpectedly when switching modes
- Controls, labels, and hover states should remain intuitive
10. Acceptance Criteria
- A theme toggle is displayed on the main interface.
- Dark mode updates the board, cards, controls, modal, and best score panel.
- The game remains fully playable in dark mode.
- The selected theme remains after browser refresh.
- Keyboard users can access and trigger the theme toggle.
- Focus indicators remain visible in dark mode.
- Light mode remains available as a toggle option.
- The game appears polished and readable in both modes.
11. Technical Notes
Recommended Implementation Approach
Use CSS variables and a theme class or data-theme attribute on the body element. This keeps the styling organized and reusable while reducing the amount of custom CSS needed across components.
Example approach:
body[data-theme="light"]body[data-theme="dark"]
Persistence
Use localStorage to store the selected theme, e.g.:
Suggested Interaction
- click toggle button to switch theme
- initialize theme on page load
- update label text or icon to reflect current mode
12. Risks and Considerations
Risk
Some elements may hard-code colors and not update properly in dark mode.
Mitigation
Review all components after implementation to ensure:
- text color contrast is sufficient
- card faces read properly
- buttons and modal backgrounds match the active theme
- focus states remain visible
13. Rollout Plan
Phase 1
Add the dark theme toggle and apply the new palette to the main interface.
Phase 2
Validate readability, contrast, and focus states.
Phase 3
Persist the theme and verify it remains after refresh.
Phase 4
Final QA across the supported browser layout and interaction modes.
14. Definition of Done
The feature is complete when:
- dark mode is available and functional
- all major UI areas support theme switching
- the selected theme persists after refresh
- theme behavior passes basic accessibility checks
- gameplay remains unaffected
15. Summary
This feature adds a dark mode to the Memory Game while preserving the existing gameplay experience. It improves comfort, readability, and modern polish without changing the core mechanics of the product.