# create labels and color palette
labels1 <- paste0(
  laender$NAME_1, ": ", round(laender$Wahlbeteiligung * 100, 1), "%"
) %>% lapply(htmltools::HTML)

pal1 <- colorBin("plasma", domain = laender$Wahlbeteiligung, reverse = TRUE)

# create map
leaflet(laender) %>%
  addProviderTiles(providers$Esri) %>% # oder $Stamen.TonerLite
  addPolygons(weight = 2, color = "black", fillColor = ~pal1(Wahlbeteiligung),
              dashArray = "4", fillOpacity = 0.5, label = labels1,
              highlightOptions = highlightOptions(weight = 3, color = "#800000",
                                                  dashArray = "", fillOpacity = .8,
                                                  bringToFront = TRUE)) %>%
  addLegend(pal = pal1, values = ~Wahlbeteiligung, opacity = 0.7, title = NULL, labels = "",
            position = "topright", labFormat = labelFormat(suffix = "%", digits = 2))