Thank you for playing our game!
There were many bugs we wanted to fix and improvements we wanted to make but unfortunately ran out of time for. We will definitely update the game to fix those bugs after the jam. For the highlighting bug, I think it's a browser issue. I ran into the same bug in Firefox, but it's fine in Google.
Also don't worry about using a calculator, I also had to use one while testing the game! Maybe we'll build a built-in calculator in a future update. It would be cool though if people do play this game and it helps improve their math skills a bit.