Adding CSS styling in the legend title in ggplot

Question

I have below ggplot

library(ggplot2)
library(stringr)
library(tidyverse)

# Create long labels to be wrapped
iris$Species = paste(iris$Species, 
                     "random text to make the labels much much longer than the original labels")

ggplot(iris, aes(Sepal.Length, Sepal.Width, colour=str_wrap(Species,20))) +
  geom_point() +
  labs(colour="Long title shortened\nwith wrapping") +
  theme(legend.key.height=unit(2, "cm"))

I am wondering if I can apply some CSS styling in the legend title. For example, I want to change font size of the word wrapping to 12, whereas remaining words with font size 10.

Any pointer will be very helpful.

Answer 1

You can use the package ggtext and the element_markdown for your legend.title with some CSS styling. You can modify to whatever you want. You can use the following code:

library(ggplot2)
library(stringr)
library(tidyverse)
library(ggtext)

# Create long labels to be wrapped
iris$Species = paste(iris$Species, 
                     "random text to make the labels much much longer than the original labels")

ggplot(iris, aes(Sepal.Length, Sepal.Width, colour=str_wrap(Species,20))) +
  geom_point() +
  labs(colour="<span style='font-size:10pt'>Long title shortened with </span><span style='font-size:12pt'>wrapped</span>") +
  theme(
    legend.title = element_markdown()
  )

Output:

As you can see the word wrapped has a font size of 12 and the other words have 10