Sudoku puzzle game, Canvas 2D, dark theme, auto-generated valid 9x9 puzzles, 3 difficulty levels (easy/medium/hard), number input via click and keyboard, conflict highlighting, timer, Web Audio API sounds, 24 national team color themes, endless mode, responsive layout, HUD overlay controls, zero external assets.
Fill the 9x9 grid so every row, column, and 3x3 box contains digits 1-9!