`page_navbar(fillable=True)` with `sidebar` is missing gap in main content area

[cpsievert]

(shinylive reprex)

In the example above, notice how there isn't any gap (i.e., padding) between the cards (when there should be).

If you remove the sidebar, gap is applied correctly.

Also worth noting that the R version of this example doesn't appear to have this bug

[gadenbuie]

Reprex code

from shiny import App, ui

app_ui = ui.page_navbar(
    ui.nav_panel(
        "Page 1",
        ui.card("Card 1"),
        ui.card("Card 2"),
    ),
    sidebar=ui.sidebar("Foo"),
    fillable=True,
    title="foo"
)


app = App(app_ui, None)