It seems that changing the main background color and also header (navbar) background color in dark mode is not possible. per this link:

• 

  CodePudding user response：

  Set the argument dark = NULL in dashboardPage():

  library(shiny)
  library(bs4Dash)
  
  shinyApp(
    ui = dashboardPage(
      dark = NULL, 
      
      title = "Basic Dashboard",
      header = dashboardHeader(),
      sidebar = dashboardSidebar(),
      controlbar = dashboardControlbar(),
      footer = dashboardFooter(),
      body = dashboardBody()
    ),
    server = function(input, output) {}
  )
  
  
  ``