Sure, here's a simple pixel RPG game implemented as a single HTML file using JavaScript:
To play the game, simply copy the above code into an HTML file and open it in a web browser. The game displays a green square representing the player character on a 400x400 pixel canvas. You can use the arrow keys to move the player character around the canvas. The character cannot move beyond the canvas boundaries. The game will update the player's position and redraw the canvas accordingly.