You should import_protomolecule first and also install the fonts on your system before trying to use this theme.

theme_expanse(base_family = protomolecule("light"), base_size = 11.5,
  plot_title_family = protomolecule("medium"), plot_title_size = 18,
  plot_title_face = "plain", plot_title_margin = 10,
  plot_title_col = expanse_cols$white,
  subtitle_family = protomolecule("light"), subtitle_size = 13,
  subtitle_face = "plain", subtitle_col = expanse_cols$mcrn_red_1,
  subtitle_margin = 15, strip_text_family = base_family,
  strip_text_size = 12, strip_text_face = "plain",
  strip_text_col = expanse_cols$white,
  caption_family = protomolecule("light"), caption_size = 9,
  caption_face = "plain", caption_margin = 10,
  caption_col = expanse_cols$white, axis_text_size = base_size,
  axis_title_family = base_family, axis_title_size = 9,
  axis_title_face = "plain", axis_title_just = "rt",
  plot_margin = margin(30, 30, 30, 30), panel_spacing = grid::unit(2,
  "lines"), text_col = expanse_cols$white,
  grid_col = alpha(expanse_cols$white, 1/2), axis_col = grid_col,
  background_col = expanse_cols$background,
  foreground_col = expanse_cols$display_blue, grid = TRUE,
  axis = FALSE, ticks = FALSE)


base_family, base_size

base font family and size

plot_title_family, plot_title_face, plot_title_size, plot_title_margin, plot_title_col

plot tilte family, face, size, margin, and color

subtitle_family, subtitle_face, subtitle_size, subtitle_col

plot subtitle family, face, size, and color


plot subtitle margin bottom (single numeric value)

strip_text_family, strip_text_face, strip_text_size, strip_text_col

facet label font family, face and size

caption_family, caption_face, caption_size, caption_margin, caption_col

plot caption family, face, size and margin


font size of axis text

axis_title_family, axis_title_face, axis_title_size

axis title font family, face and size


axis title font justificationk one of [blmcrt]


plot margin (specify with ggplot2::margin)


panel spacing (use unit())

text_col, axis_col, background_col, foreground_col

more colors to set


grid color


panel grid (TRUE, FALSE, or a combination of X, x, Y, y)


add x or y axes? TRUE, FALSE, "xy"


ticks if TRUE add ticks


There is an option hrbrthemes.loadfonts which -- if set to TRUE -- will call extrafont::loadfonts() to register non-core fonts with R PDF & PostScript devices. If you are running under Windows, the package calls the same function to register non-core fonts with the Windows graphics device.