setting default styles

[kinecology]

In your readme, I see this as a possible way to change default styles:

const wordDocument = defaultDocxSerializer.serialize(state.doc, opts, (state) => {
  return {
    numbering: {
      config: state.numbering,
    },
    fonts: [], // embed fonts,
    styles: {
      paragraphStyles,
      default: {
        heading1: paragraphStyles[1],
      },
    },
  };
});

Is styles an externalStyles, and paragraphStyles just an XML string, like this demo at docx.js?

const styles = fs.readFileSync("./demo/assets/custom-styles.xml", "utf-8");
...

Do styles have to be defined in XML? All I want to do is be able to set the default font size and the size of the headings.