change font_family for bookdown::gitbook()

Question

I am currently trying to change the font family for a gitbook I am trying to render. Below is the YAML metadata:

---
bookdown::gitbook:
  theme:
    bslib: true
    version: 4
    base_font:
      google: "Roboto"
    heading_font:
      google: "Nunito"
---

But when I render the index.Rmd file, I get the following error - Error in rmarkdown::html_document(..., extra_dependencies = c(gitbook_dependency(table_css, : formal argument "theme" matched by multiple actual arguments

Any suggestions? What am I doing wrong in providing the theme?

(I was following this link here: https://rstudio.github.io/bslib/articles/theming/index.html)