Adding a second class onto the callouts for HTML works — One usage example is to target a callout using CSS

```
::: {.callout-note .my-callout}
Hello!
:::
```

And the CSS file:

```
.callout.callout-style-default.my-callout .callout-body {
    font-size: 1.0rem;
}
```

_From a post by @jimjam-slam in https://github.com/quarto-dev/quarto-cli/discussions/4755#discussioncomment-5631059_

This works for HTML format as we pass attributes and classes, but not in revealjs format where it seems we don't. 
cscheid
2023-04-17T08:28:28Z
cderv
enhancement revealjs callouts
v1.4
open
Adding a second class onto the callouts works in html format but not revealjs format
https://github.com/quarto-dev/quarto-cli/issues/5208