Checked it out. Works good. But there are some repeating exercises. On one level I got 4 consecutive "10-8" or something similar. I think it would be better to not show duplicate exercises, at least on a single level (if it has been solved already, of course).

a tiny bit more JavaScript to focus the input field on load would go a long way

Cool! Wishlist if you’re looking for new features:

- A way to skip to higher level at the start—like maybe an Easy, Normal, Hard difficulty level like in video games.

- CSS themes to make it aesthetically neater. Like a ninja background image, you-got-it-correct animated elements, etc.

But yeah, cool hobby project for sure.

This is cool I’m literally working on something similar for words.