Sure, here's an example of a simplified version of the Flappy Bird game implemented as a single HTML file using JavaScript:
You can save the above code as an HTML file, open it in a web browser, and play the Flappy Bird game. The bird can be controlled by pressing any key on the keyboard (assuming a smartphone with virtual keyboard). The goal is to navigate the bird through the gaps in the pipes without colliding. Each successful gap passage increases the score, and collision with the pipes or the ground ends the game.