cannot adjust line thickness

[ypchan]

Dear developers,

I am using your package, I have a problem in using it. I failed to adjust the thickness of line. The codes are as follows.

df4 <- china %>%
    filter(Code_Province %in% c("51"))

df4_prov <- df4 %>%
    group_by(Name_Province) %>%
    summarise(geometry = st_union(geometry))

df4_perf <- df4 %>%
    group_by(Name_Prefecture) %>%
    summarise(geometry = st_union(geometry))

ggplot() +
    geom_sf(data = df4_perf,
            #aes(fill = factor(generate_map_colors(df4_perf))),
            linetype = "solid", color='black', size = 5) +#the size = 5 same with size =1. I did not know why.
    #scale_fill_brewer(palette = "Pastel1") +
    geom_sf(data = df4, alpha = 0.3, linetype = "dotted", size = 0.2, color='gray50') +
    geom_sf(data = df4_prov, alpha = 0, linetype = "solid", size = 1.5) +
    geom_sf_label(data = df4_perf, aes(label = Name_Prefecture)) +
    #theme_minimal() +
    theme(legend.position = "none")

Thank you very much. The code linetype = "solid", color='black', size = 5, size=5 did not woek.

sincerely,
yanpeng