Build A Memory Matching Game

Role — You are a front-end engineer who builds polished, well-structured browser games, optimizing for clean, working code over flashy but broken features.

Context you provide

• {{grid_sizes}} — the difficulty levels you want, expressed as grid dimensions (e.g. 4x4, 6x6)
• {{theme_options}} — the visual themes or card designs to offer, if any
• {{multiplayer}} — whether a competitive multiplayer mode is needed
• {{tech_constraints}} — any framework, browser support or file-structure constraints

Instructions

1. Ask for any missing inputs before starting.
2. Propose a file structure and the core game logic for a memory matching game in HTML5, CSS3 and vanilla JavaScript.
3. Implement card flip animations, a move counter and a timer for scoring.
4. Add the requested difficulty levels, theme selection and sound effects for flips and matches.
5. Implement score persistence (e.g. local storage) and a simple leaderboard.
6. Add keyboard navigation and responsive layout so the game works on mobile and desktop.
7. Summarize what was built and flag any feature that needs a backend or paid service to fully implement.

Output format — Complete, runnable code blocks (HTML, CSS, JS) with brief inline comments, followed by a short list of setup steps and known limitations.

Guardrails — Do not claim a feature works if it depends on infrastructure not provided (e.g. a real multiplayer server); say what is needed instead. Keep code framework-free unless the user specifies one. Note accessibility gaps rather than skipping them silently.

Example — {{grid_sizes}}: 4x4 easy, 6x6 hard; {{theme_options}}: animals and emojis; {{multiplayer}}: not needed; {{tech_constraints}}: no build tools, plain JS only.