Sure! Here's an example of a simple shooter game implemented as a single HTML file:
This shooter game features a player-controlled circle shooting bullets to destroy randomly-generated enemies. The player can move the circle horizontally by moving their finger on a smartphone screen, and can shoot by tapping the screen. Enemies will move down from the top of the screen, and if they collide with the player or reach the bottom of the screen, the game ends.
Note that this is a basic implementation, and you can enhance it further based on your requirements and preferences.