Nice website, only thing that bothers me is the numbers on the difficulty recalculation/halving are upside down when in the lower half of the circle. The numbers should be oriented to point towards the centre of the circle when in the lower half and away from the centre in the upper half so they're always readable without tilting your head. I'm not familliar with CSS so not sure of the best way to do this, but adding a transform: scale(-1, -1) when the number is in the lower half seems to orient the text properly.

Also, the website refreshes everytime I switch to another tab and switch back, which is a bit annoying. Infact after doing a bit more testing, it seems the website completely reloads if the window resizes as well.