The tone marks are too small! Maybe they work on the screens of duolingo web devs, but not here.
Please make the accent and tone marks bigger! I suspect that they look big enough on the screens of the web developers at Duolingo, but they do not look big enough on my 13" laptop. It is excruciating, and they are essential to learning Chinese and French. The answers are especially small, and when you tint them blue--it's even worse. I see other people complaining about this as well. UX for the win! Please fix!
You can try zooming in.