[FR] {thematic} support in `bookdown::bs4_book()`

Hello!

I want to use {thematic} with bookdown::bs4_book() to propagate the styling of the bookdown to plots, tables, etc., to generate a more cohesive look. Would it be possible to extend the use of bookdown::bs4_book() to also support {thematic}? (I had requested this feature on {thematic} before: rstudio/thematic#109)

I have tried the following approach in a bookdown project that only contains an index.Rmd file by adding thematic::thematic_rmd():

--- 
title: "A Minimal Book Example"
author: "John Doe"
date: "`r Sys.Date()`"
description: "A simple bookdown using {thematic}"
site: bookdown::bookdown_site
documentclass: book
output:
  bookdown::bs4_book:
    theme:
      bootswatch: cyborg
---

# About

```{r setup, include = FALSE}
thematic::thematic_rmd()

Here a plot:

plot(pressure)


The output looks like this:

![Screen Shot 2021-09-15 at 1 19 00 PM](https://user-images.githubusercontent.com/11433347/133505966-e1d38983-75c7-40d7-af19-45dcca7a890e.png)

i.e. the plot is not styled like the theme, and I receive the following warnings:

Warning messages: 1: thematic was unable to resolve bg='auto'. Try providing an actual color (or NA) to the bg argument of thematic_on(). By the way, 'auto' is only officially supported in shiny::renderPlot(), some rmarkdown scenarios (specifically, html_document() with theme!=NULL), in RStudio, or if auto_config_set() is used. 2: thematic was unable to resolve fg='auto'. Try providing an actual color (or NA) to the fg argument of thematic_on(). By the way, 'auto' is only officially supported in shiny::renderPlot(), some rmarkdown scenarios (specifically, html_document() with theme!=NULL), in RStudio, or if auto_config_set() is used. 3: thematic was unable to resolve accent='auto'. Try providing an actual color (or NA) to the accent argument of thematic_on(). By the way, 'auto' is only officially supported in shiny::renderPlot(), some rmarkdown scenarios (specifically, html_document() with theme!=NULL), in RStudio, or if auto_config_set() is used.



Thank you,

Stephan

rstudio / bookdown

[FR] {thematic} support in `bookdown::bs4_book()` #1273