Sticky side bar with sphinx-bootstrap-theme?

Question

I upgraded sphinx from 4.4.0 to 7.0.1 and sphinx-bootstrap-theme from 0.4.13 to 0.8.1, and, subsequently, my left sidebar is no longer sticky. As this is not my area, I am not sure what other information to provide. My goal is to have the sticky sidebar as shown at, e.g., https://guides.dataverse.org/en/latest/versions.html#guides-versions.

In conf.py I have

    html_sidebars = { '**': ['txrelations.html','my_custom_sidebar.html'] }

and in customizations/templates/my_custom_sidebar.html:

    <h3>Contents</h3>
    {{ toctree(maxdepth=2, collapse=True) }}

In customizations/bootstrap-sphinx.css I see

    /* The code below is based on the bootstrap website sidebar */
    .bs-sidenav.affix {
      position: static;
    }

I have tried changing the latter to "sticky" to no avail.