Sure, here's an example of a simple game implemented as a single HTML file using JavaScript:
In this game, it generates two random numbers between 1 and 10, and prompts the user to enter the sum of these numbers. If the user's answer is correct, it will play a "well-done" sound and display an alert saying "Well done!". If the answer is wrong, it will play a "wrong" sound and display an alert saying "Wrong answer, try again!".