Pandoc: where are CSS files for syntax highlighting code?

Question

I have a Markdown file, e.g.

---
title: Question
date: 2020-07-07
---

This is some code:

```python
def add(a, b):
    return a+b
```

and I'd like to leverage the syntax highlighting of Pandoc. This works fine:

pandoc -s --to=html5 2020-07-07-question.md

Because it includes the necessary CSS, e.g.:

<style>
    code{white-space: pre-wrap;}
    span.smallcaps{font-variant: small-caps;}
    span.underline{text-decoration: underline;}
    div.column{display: inline-block; vertical-align: top; width: 50%;}
    div.hanging-indent{margin-left: 1.5em; text-indent: -1.5em;}
    ul.task-list{list-style: none;}
    ...

However, I'm actually using Pypandoc to compile the Markdown into HTML, and then I'm including the HTML into a web page. Therefore, I'd like the CSS to be standalone, something I can reference in a file, e.g.

<link rel='stylesheet' href='/path/to/some/highlighting.css'/>

How can I do this?

Answer 1

One can inspect the default template used for HTML generation by running

pandoc --print-default-template=html5

The result will depend on your version, but should contain everything interesting. E.g., for pandoc 2.10, this will include the code

<style>
  $styles.html()$
</style>

which causes pandoc to include a file styles.html, the content of which is retrievable via

pandoc --print-default-data-file=templates/styles.html

In principle, this is what you are looking for. Now, you'll notice that there are a lot of templating commands, and the syntax highlighting CSS seems not to be included. This is because pandoc generates the CSS on the fly: the styles are stored in a way which makes it easy to use them with other outputs as well. Checkout --list-highlight-styles and --print-highlight-style.

What this means for you is that you can either just generate HTML output and copy-paste the code from there. Or you can create a helper template which just contains

$-- this is file highlighting-css.template
$highlighting-css$

Then use that template to create your highlighting.css:

pandoc --template=highlighting-css.template sample.md -o highlighting.css

Note that sample.md must contain a highlightable code block such as

~~~html
<p>placeholder</p>
~~~

This is necessary, as pandoc generates highlighting CSS only if there is something to highlight.

Answer 2

Here's a small shell script that does what @tarleb describes in his answer and cleans up after itself:

#!/bin/sh
style=${1:-pygments}
tmp=
trap 'rm -f "$tmp"' EXIT
tmp=$(mktemp)
echo '$highlighting-css$' > "$tmp"
echo '`test`{.c}' | pandoc --highlight-style=$style --template=$tmp