Keyboard and screen-reader accessibility of the radio button accordion technique is completely ruined by the use of `display: none` on the radio buttons. That could be remedied by zero-sizing them instead in one of quite a few ways. Note however that this will make Up/Down arrows switch section instead of scroll as a user might expect—that’s part of why radio buttons are not a good match for this type of widget (to say nothing of improper exposure to accessibility tech).
Keyboard accessibility is also poor due to weak and missing focus indication.
I would strongly recommend replacing the magic radio button technique with semantically and functionally appropriate elements; then, if you want opening one to close the rest, add a small snippet of JavaScript to that effect. (Then users with JS disabled will be able to open multiple sections, and that’s fine.)
The use of various CSS tricks has the side-effect that scroll position doesn’t always act in the way you might expect. I recommend augmenting such cases with small JS snippets to enhance the behaviour.