How to change bold font size to the headings of groups in pickerInput() of shinyWidgets package?

Question

I'm building an RShiny-App and now I'm formatting some parts, so they are more readable. I use pickerInput() and want to make the headingsDE and AT bold. I'm using the following R-code:

 pickerInput(inputId = "ma3DVariables", label = "Select 2 Interesting Variables", 
             choices = list('DE' = c("Munich", "Berin", "Hamburg"),
                            'AT' = c("Vienna", "Graz", "Salzburg")), 
             multiple = TRUE)

This gives me at the moment the following:

How can I make the headings bold? Any suggestions?

Answer 1

You can add custom style to a Shiny app:

tags$head(tags$style(HTML(".dropdown-header .text { font-weight: bold }")))