Multiple NavBars on Shiny Dashboard-- remove weird spacing - html

Question

I am using multiple navbars on my shiny dashboard page because I plan to create a conditional filter based on which tab is selected. Can the space between the two nav bars be removed?
Also, can the space reserved for the title be removed? I've seen some similar questions on here but I am pretty bad with CSS, so if someone could show me exactly where I can edit my code, that would be awesome.
Code:
library(shiny)
library(shinydashboard)
library(data.table)
library(dplyr)
ui <- dashboardPage(
dashboardHeader(),
dashboardSidebar(width = 325,
uiOutput("filter")),
dashboardBody(
navbarPage(header="",title=NULL,id="trythis" ,
tabPanel("BigTab1",
navbarPage(title = NULL,id="firstbar",
tabPanel("SubTab1",
dataTableOutput("table1")),
tabPanel("SubTab2"))),
tabPanel("BigTab2",
navbarPage(title=NULL,id="secondbar",
tabPanel("SubTab3",
dataTableOutput("table2")),
tabPanel("SubTab4")))
)
)
)
server <- function(input, output){
output$table1<-renderDataTable({
data<-filter(mtcars,cyl %in% input$test)
data.table(data[,1:2])
},options = list(lengthMenu = c(5, 10, -1), pageLength = 5))
output$table2<-renderDataTable({
data<-filter(mtcars,cyl %in% input$test)
data.table(data[,1:2])
},options = list(lengthMenu = c(5, 10, -1), pageLength = 5))
output$filter<-renderUI({
if(input$trythis=="BigTab1"){
selectInput("test","Test",choices = c("4","6","8"),selected=c("4","6"),multiple = TRUE)
}else{
selectInput("test","Test",choices = c("4","6","8"),multiple = FALSE)
}
})
}
shinyApp(ui = ui, server = server)
I want to remove the red, more worried about the space between the bars than the others, but the title space on the navbar is also pretty bad when you make the window smaller. Thanks in advance for any help!