Changing chunk background color in RMarkdown

Question

I would like to have a certain code chunk highlighted in a different color (e.g. red) to indicate that it is bad practice. If I was using .Rnw, I could add the chunk option background = 'red' and get what I want, but this does not seem to work in .Rmd. My guess is that I need to make a custom css stylesheet (though what the selector would be, I don't know), and maybe also create a custom hook. I'd like it to be on a per-chunk basis, not an overall change for the entire document.

Answer 1

We can use the class.source option in the code chunk header to provide custom CSS to R Markdown. This is explained in the following post:

Add a CSS class to single code chunks in RMarkdown

Putting together an example, I might set a class called "badCode" then have a bit of CSS to change the background as you might like. Here's my .Rmd:

---
output: html_document
---

```{css}
.badCode {
background-color: red;
}
```

```{r mtcars}
summary(mtcars)
```

```{r cars, class.source="badCode"}
summary(cars)
```

Answer 2

Remember markdown supports HTML outside of code blocks.

I would surround the code chunks with a div with a custom class that styled them how I wanted. This example styles the code in blue, the output in light blue

<style>
div.blue pre { background-color:lightblue; }
div.blue pre.r { background-color:blue; }
</style>

<div class = "blue">
```{r bluecars}
summary(cars)
```
</div>

```{r normal}
summary(cars)
```

Answer 3

This solution is a bit hack-y, but it works. The gist of it is to make two code chunks, swapping the {r} designator with a unique class name. Then add css code to style each chunk.

---
output: html_document
---

<style>
pre.bluecars {
    background-color: #aabbff !important;
}
pre.redcars {
    background-color: #ffbbbb !important;
}
</style>

## chunk-specific bg colors

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

- blue

```{bluecars}
summary(cars)
```

```{r, echo=FALSE}
summary(cars)
```

- normal

```{r}
summary(cars)
```

- red

```{redcars}
summary(cars)
```

```{r, echo=FALSE}
summary(cars)
```

Answer 4

I found the following way to color (code) chunks in Rmarkdown documents that I knit to PDF:

Use a pandoc highlighting scheme as a basis

pandoc --print-highlight-style pygments > my.theme

Then edit my.theme by using a regex to set all

"text-color": null

Then, you can change this property to any color you like (this one here is lightgrey)

"background-color": "#f8f8f8"

In the YAML of your .Rmd document under "pdf_document", put the following

pandoc_args: --highlight-style=my.theme

For my use case this is all I need.

Answer 5

you can also use following examples:

```{css, echo = F}
h1 { color: rgb(255, 125, 0); }
h2 { color: brown; }
div.yellow pre { background-color: lightyellow; }
div.yellow pre.r { background-color: lightblue; }
.my_pink1 { background-color: pink; }
.my_pink2 { background-color: rgb(255, 113, 181); color: white; border: 3px solid blue; }
.my_span  { background-color: orange; font-family: courier}
```

# Title 1
## Title 2

<div class = "yellow">

```{r yellow_cars1}
summary(cars)
```

</div>

```{r yellow_cars2, class.source = "my_pink1", class.output = "my_pink2"}
summary(cars)
```

Test: <span class = "my_span">change properties</span> \
Roses are $\color{red}{\text{beautiful red}}$,
violets are $\color{blue}{\text{lovely blue}}$.

read more e.g. at
Changing chunk background color in RMarkdown
https://bookdown.org/yihui/rmarkdown-cookbook/chunk-styling.html
How to change the font color?