Sure! Here's a simple game called "Virus Collector" implemented as a single HTML file:
This game features a blue cube player (controlled by arrow keys on a smartphone) and a green cube virus enemy that moves towards the player. The aim of the game is to avoid collision with the virus. When a collision occurs, an alert message saying "Game Over!" is shown.
Feel free to save this code in a single HTML file and open it in a smartphone browser to play the game.