Sure! Here's an example of a single HTML file that creates a simple game with a random emoji moving in a box. Every time the emoji hits a wall or corner, the box shrinks. The game is designed for smartphone operation and uses emoji pictograms.
To try this game, simply copy and paste the code into a new HTML file and open it in a web browser. The game box will initially be a 300x300 square, and the emoji will start moving randomly within it. Each time the emoji hits a wall or corner, the box will shrink by 10 pixels. The game will continue indefinitely, with the emoji bouncing off the walls and the box getting smaller. Enjoy playing!