Change font size of titles from facet_wrap

Reproducible example

set.seed(1)
df <- data.frame(A=rep(c("good","bad"),each=8),
                 B=rep(c("yes","no"),4),
                 C=sample(1:20,16),
                 stringsAsFactors=F) %>%
      group_by(A,B)

Question

I'd like to change the font size of the titles from facet_wrap ('bad' 'good')

ggplot(df, aes(x=B, y=C)) +
  geom_violin() +
  geom_point() +
  facet_wrap(~A, nrow=1) +
  theme_classic() + 
  theme( axis.text = element_text( size = 14 ),
         axis.text.x = element_text( size = 20 ),
         axis.title = element_text( size = 16, face = "bold" ),
         legend.position="none" )

Any ideas? Thanks!