arrow

GH-38209: [Docs] Reduce width of header items and keep header height default (small) on smaller screens (#38148)

### Rationale for this change

The Sphinx theme we have been using (PyData Sphinx Theme) has been pinned to an older version for a while now and with the https://github.com/apache/arrow/pull/36591 we have updated the code and are now using version 0.14.0 for the dev docs.

This PR fixes bugs we have encountered after the PR updating the theme has been merged.

### What changes are included in this PR?

- Have default header size for smaller screens and keep it increased for bigger screens.

* Closes: #38209

Authored-by: AlenkaF <frim.alenka@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>