No right side navigation bar in "book" pages

[brian-rose]

Some pages on the portal site use a "book" layout, e.g. https://projectpythia.org/about.html

In these, there should be a "On this page" navigation bar on the right side showing the section headings, as we have e.g. in Foundations: https://foundations.projectpythia.org/preamble/how-to-use.html

As noted in #435, the lack of this sidebar impacts the readability of longer pages.

I suspect the reason why this feature is missing from the portal site but appears on Foundations for pages that use the same theme is related to the fact that the portal is a pure Sphinx build, while Foundations (and also Cookbooks) are built with JupyterBook. I haven't dug any deeper than that.

[brian-rose]

Likely related: there is a non-functional "Toggle secondary sidebar" button on pages in both portal and Foundations. The pages behave as if the sidebar is permanently toggled "on" in Foundations and "off" in the portal.

Different default settings?