It’s possible I’m alone in this, but the textbook / vaguely “academic” style of site always comes across as messy to me. That said, I think we’re spoiled by vaporware that invests huge money into style and flashy visuals — as anyone who’s been in school during the Blackboard/Piazza era knows, education software does not have to be pretty to be popular.

maybe the layout just messed up on the resolution I looked at it with, there were boxes all over the place, the spinny thing on the main page scaled out of its bounding box. also I think it would be helpful to have some consistent design cues for which elements are interactive or what you can do with them.

if nothing else I feel each interactive canvas should have some kind of description of what you can do with it so you don't have to trial & error

I tried look at this page on an iPhone, and the figures kept resizing and the page was reflowing whenever I tried interacting with the diagrams, sometimes looking messy. That makes me thing it’s possible the parent was at an odd resolution that does look bad.