title: xaringan: Changing code background for specific chunks
body: <p>In <a href="https://github.com/yihui/knitr/issues/1333" rel="noreferrer">this</a> feature request back in 2016 Yihui shows, at the bottom, how to have different code chunks have different backgrounds in R Markdown. I've attached a screenshot of this here. Is there a way to do this with xaringan?</p>
  
  <p><a href="https://i.stack.imgur.com/wMgci.png" rel="noreferrer"><img src="https://i.stack.imgur.com/wMgci.png" alt="rmd-solution"></a></p>
  
  <p>I found <a href="https://stackoverflow.com/questions/52030224/xaringan-how-do-you-change-code-chunk-background-color">this</a> answer, which works for changing the background color for all code chunks, but I can't figure out how to modify the css so I can change the background for just a few specific chunks.</p>
  
  <p>The goal here is to have most chunks show up normally, but a few show up with a red background or similar to signify "This is bad". Any help would be appreciated.</p>