Sure, here's an example of a simple game called "Good vs Evil" implemented as a single HTML file:
This game is a simple simulator where the player (represented by a blue rectangle) tries to avoid colliding with the enemy (represented by a red rectangle). The player can control the movement of their character using the arrow keys on the smartphone. When a collision occurs, the game is reset and an alert message appears saying "Game Over!". The game is enclosed in script tags and can be played directly in a web browser by opening the HTML file.
Please note that this example is meant to provide a basic framework and can be expanded upon with additional features, levels, and graphics to create a more engaging and complex game.