I have a figure assembled with patchwork as follows:
library(ggplot2)
library(patchwork)
p1 <- ggplot(mtcars) + geom_point(aes(mpg, disp))
p2 <- ggplot(mtcars) + geom_boxplot(aes(gear, disp, group = gear))
p1 + p2 + plot_annotation(tag_levels = 'a')
How can I change the font face of tags so that the letters a and b appear in bold face?

