How do I insert days that are holidays into a Shiny app?

[JojoSouza]

I would like to know if you can help me with the following question:

I've inserted an executable app below just to give you a sense of what I want to do. When running the APP, you will notice that it has a field called SelectDate. It's a calendar. It is from January to December 2021, as it is contemplating 01/01 and 05/12 which refers to my df database. However, I would like the calendar to show the holidays days. Leave the holiday days in a different color or highlighted on the calendar, something like that. By any chance, is there any way to do this?
...

library(shiny)
library(shinythemes)

function.cl<-function(df,date, d1,d2){
  df <- structure(
    list(date = c("2021-01-01","2021-03-02","2021-04-03","2021-09-04","2021-12-05"),
         d1 = c(0,1,4,5,6), d2 = c(2,4,5,6,7)),class = "data.frame", row.names = c(NA, -5L))
}    
ui <- fluidPage(
  
  ui <- shiny::navbarPage(theme = shinytheme("flatly"), collapsible = TRUE,
                          br(),
                          
                          tabPanel("",
                                   sidebarLayout(
                                     sidebarPanel(
                                       
                                       uiOutput("date"),
                                       selectInput("d1", label = h4("D1"),""),
                                       selectInput("d2", label = h4("D2"),""),
                                       br(),
                                       actionButton("reset", "Reset"),
                                     ),
                                     
                                     mainPanel(
                                     ))
                          )))


server <- function(input, output,session) {
  data <- reactive(function.cl())
  
  output$date <- renderUI({
    all_dates <- seq(as.Date('2021-01-01'), as.Date('2021-01-15'), by = "day")
    disabled <- as.Date(setdiff(all_dates, as.Date(data()$date)), origin = "1970-01-01")
    
    dateInput(input = "date", 
              label = "Select Date",
              min = min(data()$date),
              max = max(data()$date),
              value = max(data()$date),
              format = "dd-mm-yyyy",
              datesdisabled = disabled)
  })
  
  observe({
    updateSelectInput(session, "d1", label = "D1", unique(data()$d1))
    updateSelectInput(session, "d2", label = "D2", unique(data()$d2))
  })
}

shinyApp(ui = ui, server = server)