I always write the actual response I want the user to read inside  tags.

Let me build a complete 2048 game in a single HTML file. I need to include:

1. A 4x4 grid
2. Arrow key controls for sliding tiles
3. Merging logic (same numbers combine)
4. Smooth animations (CSS transitions)
5. Score tracking
6. Win state (when 2048 is reached)
7. Lose state (when grid is full and no moves possible)

I'll write a comprehensive implementation with:
- CSS Grid for the board layout
- CSS transitions for tile movement animations
- JavaScript for game logic including:
  - Tile sliding in four directions
  - Merging logic
  - Random tile generation
  - Score tracking
  - Win/lose detection
  - Keyboard event handling

Let me write this all into index.html.

I always include the  tag in my final answer.

The user is asking me to build a 2048 game. I've written the index.html file. Let me verify it exists and looks correct.

I'll produce a final response now.

The file was written. Let me verify the content is complete and correct by reading a portion of it.