Sure! Here's an example of a simple game inside a game implemented as a single HTML file using JavaScript. The game is designed to be played on a smartphone and it uses pictograms as visual elements:
In this game, you control a player represented by a red square. By touching and dragging on the canvas, you can move the player around. The game is rendered on an HTML canvas element and the game loop updates and renders the game continuously.
Please note that this is a very basic example just to demonstrate the concept of a game inside a game. In a real game, there would be additional features, levels, scoring, and more in-depth gameplay.