Polish signs on shinydashboard

Question

I have a problem with floors in shinydashboard. When I use only shiny, everything is fine, but in shinydashboard ąand ęwritten in a different font. I tried to change the encoding of the document, but that did not help. I really don't know how to deal with this ... Could you help me?

My code is:

library("shiny")
library("shinydashboard")

ui <- dashboardPage(
    dashboardHeader(),
    dashboardSidebar(),
    dashboardBody(h1("przejścią"))
)

server <- function(input, output) { }

shinyApp(ui, server)

And visualizing my problem: