bslib color-mode

    library(shiny)
    library(bslib)
    library(titanic) # example data
    library(vcd) # mosaic plot
    library(khroma) # color palettes
    library(grid) # grid.rect

    ui <- bslib::page_navbar(
      title = "Dark Mode Demo",
      theme = bslib::bs_theme(version=5),
      bslib::nav_panel(
        title = "Base Graphics",
        bslib::card(
          bslib::card_header("Titanic: \u00dcberlebenswahrscheinlichkeit nach Klasse"),
          shiny::plotOutput("base_mosaic")
        )
      ),
      bslib::nav_spacer(),
      bslib::nav_item(
        bslib::input_dark_mode(id = "theme_toggle", mode = "light")
      )
    )

    server <- function(input, output, session) {
      # dark / light mode
      shiny::observeEvent(input$theme_toggle, {
        bslib::toggle_dark_mode(mode=input$theme_toggle)
      })

      # load only once
      titanic_dat <- shiny::reactive(
        titanic::titanic_train
      )

      output$base_mosaic <- shiny::renderPlot({
        current_theme <- bslib::bs_current_theme()
        if(input$theme_toggle=="dark") {
            bg <- bslib::bs_get_variables(current_theme, "body-bg-dark")[["body-bg-dark"]]
            fg <- bslib::bs_get_variables(current_theme, "body-color-dark")[["body-color-dark"]]
            clr <- khroma::color("dark")(2)
        } else {
            bg <- bslib::bs_get_variables(current_theme, "body-bg")[["body-bg"]]
            fg <- bslib::bs_get_variables(current_theme, "body-color")[["body-color"]]
            clr <- khroma::color("light")(2)
        }

        # base mosaicplot does not allow changing the color of the variable names, so we use vcd::mosaic
        # vcd::mosaic does not allow changing the background color, so we use grid.rect
        # vcd::mosaic does not allow to change the title color, so we don't use the main argument
        grid::grid.newpage()
        grid::grid.rect(gp = grid::gpar(fill = bg, col = NA))
        vcd::mosaic(
          formula=as.formula("~ Survived + Pclass"),
          data = titanic_dat(),
          gp = grid::gpar(col = fg, fill=clr),
          labeling_args = list(
            gp_labels = grid::gpar(col = fg),
            gp_varnames = grid::gpar(col = fg)
          ),
          newpage=FALSE # since we used grid.newpage() already
        )

      })
    }

    shiny::shinyApp(ui, server)