code: def singlehtml_sidebars(app):
      
      if app.config.singlehtml_sidebars is not None and isinstance(
          app.builder, SingleFileHTMLBuilder
      ):
          app.config.html_sidebars = app.config.singlehtml_sidebars
docs: When using a ``singlehtml`` builder, replace the
      ``html_sidebars`` config with ``singlehtml_sidebars``. This can be
      used to change what sidebars are rendered for the single page called
      ``"index"`` by the builder.