Options to change syntax highlighting theme

[KL13NT]

Marp uses highlight-js under the hood with specific highlight-js CSS for each Marp theme. Currently, there's no way to change this behaviour but overriding the whole highlighter setup as mentioned here.

We could switch out hl-js with prism-js as mentioned here. I modified the code mentioned in the issue above to use Prism instead of highlight-js. This should work.

// engine.js
const { Marp } = require('@marp-team/marp-core')
const hljs = require('highlight.js')
const hljsDefineIECST = require('highlightjs-structured-text')
const Prism = require('prismjs')

module.exports = (opts) => {
  const marp = new Marp(opts) // marp initialization in scripts

  // Use custom highlight.js instance in Marp highlighter
  // The following is exactly same as https://github.com/marp-team/marp-core/blob/883e1d75ddf0bdf26a00cafd4f58d94a26fe4949/src/marp.ts#L92-L99
  marp.highlighter = (code, lang) => {
    if (Prism.languages[lang]) {
      return Prism.highlight(code, Prism.languages[lang], lang);
    }
    return code
  }

  return marp
}