How to create a pretty facet-boxplot with custom fonts

Required R libraries:

if(!require(tidyverse)){install.packages("tidyverse");library(tidyverse)} # for ggplot2 function
if(!require(gapminder)){install.packages("gapminder");library(gapminder)} # for sample data
if(!require(showtext)){install.packages("showtext");library(showtext)} # to import fonts

Add fonts in R session

font_add_google("Karla", "Karla") # adding local font
font_add(family = "Helvetica", regular = "C:/Windows/Fonts/Helvetica 400.ttf")
# Adding from Google fonts
font_add_google("Roboto Slab", "Roboto Slab") # adding font from the web/google font
font_families()
## [1] "sans"         "serif"        "mono"         "wqy-microhei" "Karla"       
## [6] "Helvetica"    "Roboto Slab"

Define theme for Boxplot and fonts

themeBox <- function(base_family = "sans", exFont, ...){
    theme_bw(base_family = base_family, ...) +
        theme(
            panel.grid = element_blank(),
            plot.title = element_text(size = 8),
            axis.ticks.length = unit(-0.05, "in"),
            axis.text.y = element_text(margin=unit(c(0.3,0.3,0.3,0.3), "cm")),
            axis.text.x = element_text(margin=unit(c(0.3,0.3,0.3,0.3), "cm")),
            axis.ticks.x = element_blank(),
            aspect.ratio = 1,
            legend.background = element_rect(color = "black", fill = "white"),
            text = element_text(family=exFont)
        )
}

Plot the boxplots of Average Life Expectancy

ggplot(gapminder, aes(x = continent, y = lifeExp, fill = continent)) +
    facet_wrap(~year) +
    geom_boxplot(linetype = "dashed") +
    stat_boxplot(aes(ymin = ..lower.., ymax = ..upper..), outlier.shape = 1) +
    stat_boxplot(geom = "errorbar", aes(ymin = ..ymax..)) +
    stat_boxplot(geom = "errorbar", aes(ymax = ..ymin..)) +
    scale_y_continuous(name = "Average Life Expectancy") +
    scale_x_discrete(labels = abbreviate, name = "Continent") + themeBox(exFont = "Karla")

Links:

1. Boxplot customization