system
Given the following post, respond as if you're commenting on Reddit:
human
Why is my frosted notebook cover transparent when close to an object, but opaque at distances?

I was in class and I realized that as I opened my notebook cover, the text underneath became rapidly out of focus. The cover to the notebook is a frosted plastic. When the cover is closed and the plastic is directly above the text, everything is easy to read. Once the cover is a distance of a few centimeters from the page, nothing below can be made out.

I assume this is based upon some refraction principle, but I could not find a good explanation anywhere.
gpt
the cover refracts light at different angles (most likely due to surface roughness).  thus, at close distances, rays aren't bent much, but when the distance between the medium and the subject are increased, increased refraction blurs the image.