It was quite easy to dismiss by accident. I've added some positional and
time based lenience with numbers that feel good to me. Open to
discussion on whether both are required and if the numbers feel good.
Going forward, at some point, we'll likely want to standardise this
across to other expand-on-hover elements (like player load overlays).
Addresses https://github.com/ppy/osu/discussions/32368.
The +2 for the top isn't really needed for the original purpose as content fades out now, but visually, having the header and content spacing looks more correct.
The content is already padded enough to have the scrollbar sit on top.
Having the content change padding when the scrollbar appears gives an
unpleasent experience (especially when the scrollbar is hidden at first
but the user increases the content's height by clicking on a dropdown or
something)