I love these simple web games! Great idea. One way to improve it is to add some more juice when you answer a question. Right now, the text in the number just swaps to the next question, so any sort of small visual feedback will help first time players get it more.

I also like to make these small web mini games on the side. Here's one where you guess the year that famous events happened: https://guess-the-year.davjhan.com/