Create a single-file HTML Tetris game with these specifications:

1. **7 country flag blocks** — each tetromino shape has its own unique flag:
   - I-piece: Korea 🇰🇷 (red/blue circle on white)
   - O-piece: Japan 🇯🇵 (red circle on white)
   - T-piece: China 🇨🇳 (red with yellow star)
   - L-piece: USA 🇺🇸 (blue corner with star, red/white stripes)
   - J-piece: UK 🇬🇧 (blue with red/white cross)
   - S-piece: France 🇫🇷 (blue/white/red tricolor)
   - Z-piece: Switzerland 🇨🇭 (red with white cross)

2. **Draw simplified flag patterns** on each 30×30px block using canvas.

3. **Game features**:
   - Standard 10×20 grid, 7 tetromino shapes
   - Ghost piece (transparent preview of drop position)
   - Next piece preview panel
   - Score, lines cleared, and level display
   - Level increases every 10 lines (faster speed)
   - Scoring: 1 line=100, 2=300, 3=500, 4=800 (×level)

4. **Controls**:
   - Arrow keys: left/right move, up=rotate, down=soft drop
   - Space: hard drop
   - Touch support for mobile (swipe + tap to rotate)

5. **Side panel**: Score, Lines, Level, Next piece preview, 7-nation legend showing which flag = which shape, controls reference.

6. **Style**: Dark background (#0a0a1a), modern UI with rounded corners.

7. **Single file**: Everything (HTML, CSS, JS) in one file. No external dependencies.