Sure! Here's an example of a simple first-person shooter game set in the 1700s, implemented as a single HTML file:
This game sets up a game canvas, allows you to control the player's movement using the "WASD" keys, and aims using the mouse cursor. The player is represented by a black square, and the mouse cursor is shown as a red crosshair. You can enhance this basic game by adding shooting mechanics, enemies, and other gameplay features.