Create a complete falling-blocks puzzle game in a single self-contained HTML file. No external libraries, no internet resources, no images: everything inline (HTML, CSS, JavaScript, canvas rendering).

Requirements:

- 10 wide by 20 tall playfield rendered on a canvas.
- Seven distinct piece shapes, each made of four squares, each with its own color.
- Controls: left/right arrows move, up arrow rotates, down arrow soft-drops, spacebar hard-drops.
- Rotation must respect walls and stacked blocks (no clipping through anything).
- Completed horizontal lines clear, rows above fall down, and clearing multiple lines at once scores more.
- Score, lines cleared, and level displayed. Speed increases with level.
- Next-piece preview box.
- Game over when the stack reaches the top, with a visible game-over state and a restart key.
- Clean, readable dark visual style.

Output only the complete HTML file.