Sure, here's an example of a simple game implemented as a single HTML file using JavaScript. The game consists of a blue square and a red circle. If you click on the blue square, you win, and if you click on the red circle, you lose.
In this game, the blue square and the red circle are represented as `div` elements styled using CSS. The `cursor: pointer` property ensures they appear clickable.
The JavaScript code uses `addEventListener` to listen for click events on each element. When you click the blue square, it displays a message saying "You win!" with an alert box. Similarly, clicking the red circle displays a message saying "You lose!".