Print CSS: avoid page break in some relevant cases

[rjoly]

While printing a Sphinx documentation page as PDF, I noticed that a simple list (<ul>) was separated on two successive pages.

I think simple CSS print rules could improve that kind of issues (avoid break inside a list, but also inside or after a hX title, etc.).

You can see PR #519 for an implementation proposal.

[hmaarrfk]

Thank you for helping on this point!!!

I noticed that today it seems that headers and even text can be cut midway through.

To recreate:

1. Firefox
2. Linux (Ubuntu 24.04)
3. Go to https://pradyunsg.me/furo/kitchen-sink/generic/
4. Print
   You can see in the screenshot that the text Some menu ‣ Some sub menu 1 ‣ Some sub menu 2 ‣ Some sub menu 3 is literally cut between two pages.

I'm no CSS expert (or even a novice) so I can't contribute with code, but I will say that the ability to print is somewhat nice in science when you can always use an other screen to learn about something new.

[pradyunsg]

Along with #519, I've also added fd3f422 in response to the feedback that @hmaarrfk just shared.

[hmaarrfk]

Thanks for the quick fix. does it make sense to add tr to that same line? I'm trying your main branch locally and i noticed that I had a table row that was cut off in the middle in the same way.

I tried to make the modification but it didn't seem to work maybe there is some caching issue locally for my testing.