How to change CSS classes and style for nav tabs after bslib nav_insert?

Currently for the bslib package, a nav_insert() into a page_navbar does not pass along the same CSS classes as it does for a regular tab-pane, as noted in this issue posted to the bslib Github repo.

The reprex provided by the OP is the following:

library(shiny)
library(bslib)

ui <- page_navbar(
  id = 'nav',
  nav_panel('Page 1',
            card("Content 1")))

server <- function(input, output, session) {
  nav_insert(id = "nav",
             nav = nav_panel('Page 2',
                             card("Content 2")))
}

shinyApp(ui, server)

The newly inserted tab “Page 2” does not have the same css classes as the “Page 1” tab, namely html-fill-item html-fill-container bslib-gap-spacing.

Is there a way, perhaps, to add those classes after the insert? I tried using runjs($('[data-value=Page 1]').addClass('html-fill-item')) (and several iterations of it) in the server but that did not work.

A very trivial JSFiddle demo shows the idea of the basic working syntax.

Any ideas would be very much appreciated! Thanks.