问如何在闪亮的平板之间消除空间？

EN

#install.packages("shinythemes")
#https://shiny.rstudio.com/articles/tabsets.html
#https://rstudio.github.io/shinythemes/

library(shiny)
library(shinythemes)
# Define UI for random distribution app ----
ui <- navbarPage(
  theme = shinytheme("flatly"),
  "CHIP",
  tabPanel("Plot",
           sidebarLayout(
             # Sidebar panel for inputs ----
             sidebarPanel(
               radioButtons(
                 "dist",
                 "Distribution type:",
                 c(
                   "Normal" = "norm",
                   "Uniform" = "unif",
                   "Log-normal" = "lnorm",
                   "Exponential" = "exp"
                 )
               ),
               
               br(),
               sliderInput(
                 "n",
                 "Number of observations:",
                 value = 500,
                 min = 1,
                 max = 1000
               )
               
             ),
             mainPanel(tabsetPanel(
               type = "tabs",
               tabPanel("SubA1", plotOutput("plot")),
               tabPanel("SubA2", tags$p("In subA2")),
               tabPanel("SubA3", tags$p("In subA3"))
             ))
           )),
  tabPanel(
    "SubTabs",
    tabsetPanel(
      type = "tabs",
      tabPanel("SubB1", tags$p("In subB1")),
      tabPanel("SubB2", tags$p("In subB2")),
      tabPanel("SubB3", tags$p("In subB3"))
    )
  ),
  tabPanel("SubNav", style='margin-top: -21px',
   
   navbarPage("SubNav",
     tabPanel("SubNav1", tags$p("In SubNav1")),
     tabPanel("SubNav2", tags$p("In SubNav2")),
     tabPanel("SubNav3", tags$p("In SubNav3"))
   )
  )
)
server <- function(input, output) {
  d <- reactive({
    dist <- switch(
      input$dist,
      norm = rnorm,
      unif = runif,
      lnorm = rlnorm,
      exp = rexp,
      rnorm
    )
    
    dist(input$n)
  })
  output$plot <- renderPlot({
    dist <- input$dist
    n <- input$n
    
    hist(
      d(),
      main = paste("r", dist, "(", n, ")", sep = ""),
      col = "#75AADB",
      border = "white"
    )
  })
  
}
shinyApp(ui, server)