Multiple ggplot legends: How do you adjust one of them?

I would like to access only of the legend below, carb and setting the font size to 20. How can I do that. The code below changes both legends.

library(tidyverse)

ggplot(mtcars, aes(x = mpg, y = disp, color = carb, shape = as.factor(am))) +
  geom_point() +
  theme(legend.title = element_text(size = 20))

>Solution :

You can set individual theme elements for a legend inside the function guides(). In your case, the legend for carb is a colorbar mapped to the color aesthetic, so we can do

ggplot(mtcars, aes(x = mpg, y = disp, color = carb, shape = as.factor(am))) +
  geom_point() +
  guides(color = guide_colorbar(
           theme = theme(legend.title = element_text(size = 20))
    )
  )