Image placeholder in Xaringan - r

Question

I am using the xaringan library from Yihui in R to create a custom template for a presentation.
Part of this is creating custom body slides as pictured below.
I then use custom CSS for the headers and body:
.body-yellow > h2 {
font-size: 42px;
text-transform: uppercase;
padding-left:
}
And then just type in rmarkdown something like:
---
class: body-yellow
# Hello
## world
Hello world
This then populates the slide.
My question is, is there a way to create a placeholder for the image shown in the template above that I could adjust in the rmarkdown code itself?
I am imagining code like:
---
class: body-yellow
background-images: url(./img/my_new_custom_image.png)
# Hello
## world
Hello world
And the relevant adjustment in CSS:
.body-yellow > image {
background-images: PLACEHOLDER
position:right
}
Which will change the image as follows:
Excuse my CSS ignorance, but I am only starting to dabble in this area.

Answer 1

You can set a global background image for the body-yellow class, and override it with the background-image attribute on a particular slide. Here is a minimal example:
---
title: "Test"
output:
xaringan::moon_reader:
nature:
ratio: "16:9"
---
class: body-yellow
```{css, echo=FALSE}
.body-yellow > h2 {
font-size: 42px;
text-transform: uppercase;
padding-left: 50px;
}
.body-yellow {
background-image: url(https://i.stack.imgur.com/OSrg8t.png);
background-size: contain;
}
```
## Default background
---
class: body-yellow
background-image: url(https://i.stack.imgur.com/X1C2Bt.png)
## A custom background