Sure, I can help you create a simple game in a single HTML file using JavaScript. Here's an example code that you can use as a starting point for your game:
In this game, there is a particle represented by a red circle bouncing around inside a canvas. The particle moves horizontally and vertically, bouncing off the walls of the canvas. The `updateGame` function is responsible for clearing the canvas, drawing the particle, and updating its position. The game loop is started using `setInterval` function with a 10ms interval.
Feel free to modify the code and add more features, levels, or interactions to make it a complete game.