EPUB with multiple --css causes duplicate IDs in content.opf

[nybblr]

To reuse styling between my web and epub versions, I split up my styling into several files and add them with --css:

pandoc \
  -f json \
  --standalone \
  --css publish/fonts.css \
  --css publish/typography.css \
  --css publish/highlight.css \
  -o build/book.epub \
  ...

I'm using Pandoc 2.7.2. The resultant content.opf file has this:

    <item id="style" href="styles/stylesheet1.css" media-type="text/css" />
    <item id="style" href="styles/stylesheet2.css" media-type="text/css" />
    <item id="style" href="styles/stylesheet3.css" media-type="text/css" />

The ePub opens fine in Calibre/iBooks, but since each stylesheet gets the same ID of style, it ticks off validators and is causing conversion to MOBI to fail for Kindle readers.

Is --css meant to be used multiple times in this way? Would it be enough to generate unique ids, or do the stylesheets need to be concatenated?

I thought I'd be clever and use a named pipe to concatenate them first, but apparently it interferes with processing a JSON AST from stdin.

process-that-generates-json-ast | pandoc \
  -f json \
  --standalone \
  --css <(cat publish/{fonts,typography,highlight}.css) \
  -o build/book.epub \
  -

[jgm]

Yes, --css is meant to be usable in this way. The duplicate style is probably leftover from when we only allowed one CSS file. I can fix.