chunk option class.source to add CSS class to flaired code

[dcossyleon]

Hello!

I'm interested in adding a CSS class to the flaired code chunk in my learnr Rmd. To do this, I have tried using the code chunk option class.source.

---
title: "Flair Test in LearnR"
output: learnr::tutorial
runtime: shiny_prerendered
---

```{r setup, include=FALSE}
library(learnr)
library(flair)
library(tidyverse)
```

```{r how_to_pipe, include = FALSE}
iris %>%
  group_by(Species) %>%
  summarize(mean(Sepal.Length))
```

```{r, echo = FALSE}
decorate("how_to_pipe", class.source = "r") %>% 
  flair("%>%")
```

But the outcome is this error:

Quitting from lines NA-5 (Lesson1.Rmd) 
Error in eval(x, envir = envir) : object 'r' not found
Calls: <Anonymous> ... process_group.block -> call_block -> eval_lang -> eval -> eval
Execution halted

I have also tried this chunk option with the decorate_code() function. In that case the .Rmd does knit, but the flaired chunk and its output disappear. I am working in LearnR, but this chunk option is similarly unrecognized in regular .Rmd, too.

Specifically, I am trying to add this CSS class so that I can restore the grey-background styling that seems to be stripped in flaired code chunks within LearnR (which may or may not be a related issue?):

Adding"class=r" to the <pre> tag containing the chunk content restores the default grey background that easily distinguishes it from other output like messages, warnings, etc. which have a white background)