如何在tabItem for Shinydashboard中删除列布局之间的空格

library(shiny)
library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
    tags$head(
      tags$style(HTML("
        .col-sm-4 {
          padding-right: 0px;
          padding-left: 0px;
        }
      "))
    ),
    tabItems(
      tabItem(tabName = "example",
              fluidRow(
                column(width = 4,
                       box(title = "Column 1", "Content of column 1")),
                column(width = 4,
                       box(title = "Column 2", "Content of column 2")),
                column(width = 4,
                       box(title = "Column 3", "Content of column 3"))
              )
      )
    )
  )
)

server <- function(input, output) { }

shinyApp(ui, server)