DOC: collect feedback on new sphinx documentation theme
As discussed in https://github.com/pandas-dev/pandas/issues/15556 and activated in https://github.com/pandas-dev/pandas/pull/28623, the development docs are using a new sphinx documentation theme (for now developed in https://github.com/pandas-dev/pandas-sphinx-theme/).

You can see it in action at https://dev.pandas.io/docs/user_guide/index.html

But as with all new things there will be some rough edges / certain workflows that were easier before / things you don't like / ... with the new theme. 
So feedback is very welcome! We can use this issue to collect feedback in this repo (and otherwise specific issues can also be opened at https://github.com/pandas-dev/pandas-sphinx-theme)

For the next release, I think most structural blockers are solved (search works now, tables are not completely ugly, second navigation level in left sidebar is not hidden anymore). But there are certainly a lot of improvements to be made regarding styling (typography, styling / coloring of inline code and links, ... width of the page) and mobile responsiveness. 
In https://github.com/pandas-dev/pandas-sphinx-theme/pull/32 I am trying out some basic styling for indicating the current active navigation items.