No it isn't octagon. It is a triangle on top of rectangle (about cover)
Viewing post in Sharp versions of chests comments
but the cover looks like half of an octagon, like in the round version it looks like half a circle.
if we call the ‘a semicircle on a rectangle’ version ‘round’, i don’t see why we shouldn’t call the ‘a pentagon on a a rectangle’ version ‘octagonal’.