Here's an example implementation of a Pac-Man game in a single HTML file using JavaScript:
This implementation sets up a simple Pac-Man game with a Pac-Man character (represented by a yellow circle) and food elements (represented by white dots). The game allows the Pac-Man to move using the arrow keys on a smartphone or computer, and checks for collisions between the Pac-Man and food elements. When a collision occurs, the respective food element disappears.
Note: This is a basic implementation and can be expanded upon to include additional game mechanics, levels, ghosts, and scoring functionality.