Sure! Here is an example of a single HTML file that implements a simple game using a rotating cube and a key pictogram. The game can be played on a smartphone.
When you run this HTML file in a browser, it will display a canvas element with a rotating blue cube at the center of the screen. The cube will rotate clockwise when you touch/hold the screen (on mobile) or click/hold the mouse button (on desktop). There is also a yellow key (`🔑`) at the top-right corner of the screen. If the cube touches the key, it will be collected, and the key will disappear from the screen.