How to round the edges and make a shadow in a pillow?

Question

Python

Hello everyone, implemented the placement and slope as shown in the image.
Now you need to round the edges and make a shadow
I looked at the following methods

PIL.ImageDraw.Draw.arc(xy, start, end, fill=None)
PIL.ImageDraw.Draw.point(xy, fill=None)

In my opinion, it’s too confusing and there should be a way to implement it easier than pixel by pixel or draw an arc, what do you advise?
Has anyone done a similar task?