Center Navbar Tab text with flatly theme

ui <- shiny::bootstrapPage(
    
    shiny::tags$head(
        # Include custom CSS
        includeCSS("styles.css")
        
    ),
    
    
    shiny::navbarPage(
        
        title = "Test",
        collapsible = TRUE,
        theme       = shinythemes::shinytheme("flatly"),
        
        shiny::tabPanel(
            "Map"
        )
    )
    
    
    
)

server <- function(input, output, session) {   
    
}

shinyApp(ui, server)

CSS

.container-fluid {
  height: 80px;
}

.leaflet-top .leaflet-control {
    margin-top: 40px;
}

.navbar-nav li a {
  height: 80px;
}

How do I center the Map text vertically in the navigation tab? With the default theme, I get it to work, however, with the flatly theme I cannot get it centered.