Sure! Here's an example of a simple shooting game implemented as a single HTML file:
This game allows you to control a player character (represented by a blue rectangle) using left and right arrow keys. The objective is to shoot down the green enemy rectangles using the spacebar. Your score increases each time you successfully hit an enemy. The game ends when an enemy reaches the bottom of the canvas.
Please note that this is just a basic example and can be further enhanced with additional features, levels, and graphics as per your requirements.