how do I add curly brackets outside of ggplot??

[nbaes]

Would anyone know/be able to direct me to good source on how to add brackets to image 2 to mimic image 1?

Image 1:

Image 2:

area_fig <- ggplot(df_long, aes(x = year, y = index, fill = topics2)) + 
  geom_area() +
  theme_classic() +
  xlab("\nYear") +
  ylab("Index\n") +
  scale_x_continuous(breaks = seq(1970,2017,2)) +
  scale_y_continuous(breaks = seq(0.00,1.00,0.1)) +
  theme(axis.text.x=element_text(angle = 45, hjust = 1)) +
  labs(fill = 'Topics') +
  scale_fill_manual(values = c("lightgrey", "grey",                                                                # G
                                            "#ccfefe", "#ccfe99",                                                  # F
                                            "#c905fb", "#714299",                                                  # E
                                            "#f9fcd0", "#f0f920", "#fec81f", "#fe9b2d", "#fe3502",                 # D 
                                            "#DAF2C7", "#99ff99", "#66ff33", "#33cc33", "#669900", "#336600",      # C                                
                                            "#9dc3e6", "#4777ef"      ,                                            # B
                                            "#fbe1e5", "#f4b2bb", "#ff7c80", "#ff4747", "#ff0000", "#a8041b")) +   # A    
  theme(legend.title = element_text(size = 7),
        legend.key.size = unit(0.3, 'cm'), 
        legend.key.height = unit(0.3, 'cm'),
        legend.key.width = unit(0.3, 'cm'),
        legend.position = 'right',
        legend.text=element_text(size = 6.5),
        legend.text.align = 0) +
  scale_y_continuous("",breaks=c(0.8, 1.0), labels = "High types" ) 
  
print(area_fig)

[nirgrahamuk]

I think the lemon package could do this potentially. thought style wise its brackets are square not curly.