The UX is awful - I bailed out at 25/100 JUST IN LEVEL ONE (BASICS)

Might I suggest adaptive difficulty? After getting 10, 15, 20 correct in a row it should scale up the difficulty immediately, rather than waiting for 100 in the basic level 1...

Check button hidden under the URL bar thing in safari, progress bar hidden when scrolling check button in view. In between endless whitespace.