Custom CSS classes are ignored

[wleoncio]

Summary

Marp CLI doesn't seem to recognize some custom CSS elements which Marp VSCode does

MRE

test.md

---
marp: true
theme: test
---
This presentation is <b class=superbold>BLINDING</b>!!!

test.css

/* @theme test */
@import 'default';

section {
	color: rebeccapurple;
	background: olivedrab;
}
b.superbold {
	font-weight: bolder;
	font-size: 2em;
}

Terminal command

marp test.md --theme test.css

Observed output

So the section customizations are properly parsed, but the superbold b class isn't.

Expected output

Additional comments

The latter is the output from the Marp: export slide deck... command on VSC. I tried to discover what command VSC uses so I could try to use it on the CLI as well, but I don't know where to find this.

I tried exporting to PDF, but the output is the same. I've also tried playing around with repositioning the CSS files (between its original themes/ location and the working directory of the md file), using the --theme-set switch, but nothing changed.

I may be doing something improperly here, my CSS skills are quite rudimentary.

[yhatt]

Just add --html option.

Both of Marp for VS Code and Marp CLI do not allow HTML by default for security reason. (https://github.com/marp-team/marp-vscode#enable-html-in-marp-markdown) That's also reason why <b> tag didn't work.

[wleoncio]

Nice, that does it indeed. I am a bit confused, though, because some HTML is supported by default (like <br>), though I do see the difference between an "innocent" line break and a custom class.

I also didn't consider using --html because I thought it was redundant with an HTML output. Maybe the README file should read something like "Enable or disable special HTML tags"?

[yhatt]

In other words, Marp specially allows only <br> tag because this is useful for line break(s) within fitting header: # <!--fit--> Fitting<br />header.

Marp will convert line breaks in paragraph into <br> (and CommonMark paragraphs have syntaxes for hard line break even if not) so we think typically <br> does not have to use in the most cases.