[Bug]: navbar_options behavior inconsistent with R Shiny and Python Docs

[Steven314]

Component

UI (ui.*)

Severity

P2 - Medium (workaround exists)

Shiny Version

1.3.0

Python Version

3.13.2

Minimal Reproducible Example

from shiny import App, ui

# https://shiny.posit.co/py/api/core/ui.navbar_options.html#navbar-style-with-bootstrap-5-and-bootswatch-themes
app_ui = ui.page_navbar(
    title = "Title",
    theme = ui.Theme(
        # version = 5,      # throws syntax error
        preset = "journal"
    ),
    navbar_options = ui.navbar_options(
        # class = "bg-primary", # throws syntax error
        "bg-primary",           # gives red navbar with black text
        theme = "dark"
    )
)

def server(input, output, session):
    pass

app = App(app_ui, server)

Behavior

Per the example in the docs (only I'm using the journal theme instead of flatly), I believe I should be able to pass class to ui.navbar_options(), but that throws an error about invalid syntax at class. Likewise for version = 5 in ui.Theme(). By removing version = 5 and class (but leaving "bg-primary") I get a result that runs, but is not consistent with what I believe is the R equivalent.

R Example

# R: 4.4.2
library(shiny) # 1.10.0
library(bslib) # 0.9.0

ui <- page_navbar(
    title = "Title",
    theme = bs_theme(preset = "journal"),
    navbar_options = navbar_options(
        class = "bg-primary", 
        theme = "dark"
    )
)

server <- function(input, output, session) {
    return(NULL)
}

shinyApp(ui, server)

This gives a navbar with white text on light red just like the journal Bootswatch page; that is the behavior I expect. The Python version (as best I can figure out) gives a light red navbar, but with dark text.
To my understanding this does not match the docs where it says:

The navbar's white text is controlled by the data-bs-theme="dark" attribute, which is used by Bootstrap for light text on a dark background.

Switching theme = "dark" to theme = "light" doesn't seem to have any effect here either.

Error Messages (if any)

Environment

Windows 10
R 4.4.2

[gadenbuie]

In Python, class is a reserved keyword, so you'll need to use class_ = "bg-primary". If that doesn't work, let me know and I'll take another look.

[Steven314]

I was vaguely aware of the class_ trick from somewhere, but that doesn't have any visual change from omitting navbar_options() entirely.

By inspecting the HTML I found this:

The following results in a class of navbar-inverse attached to the nav:

app_ui = ui.page_navbar(
    title = "Title",
    theme = ui.Theme(preset = "journal"),
    navbar_options = ui.navbar_options(
        class_ = "bg-primary",
        theme = "dark"
    )
)

That produces an off-white navbar with dark text. (Using theme = "light" produces the class navbar-default and the same appearance.)

Which is visually the same as below, but the below has a class of navbar-default on the nav.

app_ui = ui.page_navbar(
    title = "Title",
    theme = ui.Theme(preset = "journal")
)

I think the inverse class is what you'd expect with theme = "dark", but bg-primary is not applied.

[gadenbuie]

Thank you for the reprex and issue @Steven314! We just merged #1942 which fixes the issue (and will be in the next release of Shiny). In the mean time, you can use the dev version of Shiny from GitHub:

uv pip install git+https://github.com/posit-dev/py-shiny.git