Sure, here's a simple shooter game implemented as a single HTML file using JavaScript and enclosed in script tags:
This code sets up a simple shooter game where the player controls a character with left and right arrow keys and shoots bullets with the spacebar. The goal is to shoot down the enemies and earn points. If the player collides with an enemy, the game ends and the score is displayed. The game features a cyberpunk style through the use of colored rectangles. Feel free to modify the code and add more detailed graphics or gameplay elements to suit your needs.