Feature request: custom theme for a single slide

[coorasse]

I see that currently is possible to define a scoped style for a single slide with #94
this forces us to put CSS in the markdown file, making it less readable.
Since there is already support for custom CSS theme files, it would be great to assign a CSS class to a single slide and move the CSS in the theme file.
Adding a custom class to the section would be great.

[yhatt]

We have already supported defining custom class to a single slide through class local directive (with spot directive, an one of local directive usage).

https://marpit.marp.app/directives?id=styling-slide

/* @theme your-theme */

section {
  background: white;
}

section.red {
  background: red
}

---
theme: your-theme
---

# Regular page

---
<!-- _class: red -->

# Red background

@coorasse Would you have any problem that is not enough this usage?

[coorasse]

Hi, thanks for your feedback. I tried your approach and the result is what I expect.
What I was missing was the section.myclass { ... } part in the CSS.
I previously defined only .myclass { ... } and this was not working.