It should work on mobile browsers (though I haven't tested yet).

Seems to have an issue in Safari on iPad - there’s no way to submit my guess. The shapes highlight but then nothing happens. The timer just keeps running. I’m pretty sure I’ve selected correctly.

Not on iOS — just a gray background with the centered “code” link to the repo. No shapes, no interactivity.

Tried on Android chrome. I select two shapes which I'm pretty sure match and nothing happens. The only thing on the screen is a "code" hyperlink. Is there supposed to be a "accept" or "go" button or something?

There's no "accept" button, it should move to the next set when the two correct shapes are selected. But as someone else pointed out in this thread there may be multiple matching pairs - looking into it.

Works well on iOS on iPhone.

I like it. Great fun, thanks.

I only see a tiny “code” link on iOS, rest of the page is blank (gray).

Works fine on mobile for me. Fun game!