This fix makes the items in live examples take unnecessarily large space on Windows, though:

The core issue here is that MacOS uses overlay scrollbars whereas Windows uses classic ones. CSS Overflow Module Level 4 actually proposes to add the always value to scrollbar-gutter to solve the very problem this PR tries to fix, but Apple itself, as mentioned in the spec, is reluctant to add this value.

I see, thank you for your feedback and the link to the spec as well as the explanation about the unfortunate Apple exception.
I would tend to think that extra space around scrolled content is preferable than not seeing the content as you scroll - the latter makes it difficult to take in what is written inside the examples. But I'll close this PR if this solution is not acceptable or you prefer to wait for a conclusion on the spec that Apple adheres to

Solved this issue locally by changing the system settings for scrollbars: