WEB: Unpin pydata sphinx theme
- [x] closes #46615 (Replace xxxx with the Github issue number)
- [x] closes #42744 (Replace xxxx with the Github issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Is there a way to test the docs served by the website locally?

Not sure if you've seen that this needs to be updated if we unpin the theme version:
```
WARNING: `generate_nav_html` is deprecated and will be removed.Use `generate_toctree_html` instead.
```

Also, I think it's a better practice to not include the domain in internal links (in a link in a page hosted at pandas.pydata.org, use `/foo/bar.html` instead of `https://pandas.pydata.org/foo/bar.html`). If for whatever reason we host this under a different domain (a dev server, change of domain we use, a reverse proxy...), then having the domain make things way more difficult. @phofl did you check if we're getting the dark theme out of the box with the new theme? If we do, feel free to add #42744 to the list of issues this closes in the description.

Btw, I think it'd be nice to get this in for the release. I added the 1.5 milestone for now. If you want me to continue the work on this and see what's wrong with the CI, just let me know. Changed the link, is this what you were referring to?

Yes, we get the dark theme ootb Not sure if the docs are building, the last one was cancelled Thanks @phofl and @datapythonista for the review. I guess we'll need to update the `versions.json` when 1.5 is released. @datapythonista @phofl please see #49811 as a potential solution for a issue raised due to this we think (@tehunter).