Make a navigation list panel taller in shiny-CodePudding

Here is a simple example of a navigation list panel:

library(shiny)

ui <-  fluidPage(
titlePanel("Navlist panel example"),

    navlistPanel(
      "Header",
      tabPanel("First",
               h3("This is the first panel")),
      tabPanel("Second",
               h3("This is the second panel")),
      tabPanel("Third",
               h3("This is the third panel"))
    )

)

server <- function(input, output) {
}

shinyApp(ui, server)

I need the well (AKA the grey rectangle with rounded corners that is around the navigation list) to be taller and expand to take the white space marked by the red rectangle:

PS: be aware that you can have multiple rows in your app