I change your 'bs_add_rules ' a little bit, now your code works as you expected.

theme = bs_theme(bg = "black",fg = "white") %>%
 bs_add_rules(".accordion-title{")%>%
 bs_add_rules(" color:red;") %>%
 bs_add_rules(" front -family:'Lucida Console','Courier New',monospace;") %>%
 bs_add_rules("}")