Sure! Here's a simple implementation of the game Flappy Bird using HTML and JavaScript, enclosed in script tags for a single HTML file:
To play the game, simply save the above code into an HTML file (e.g., `flappybird.html`) and open it in a web browser. The game will be playable on smartphones as well. The bird can be controlled by tapping/clicking and it should avoid hitting the green obstacles. The score will be displayed at the top-left corner, and the game will end if the bird hits an obstacle or goes off the screen. You can play the game multiple times, as it will restart automatically after game over.