Back to Error DirectoryW3C EPUBCheck Standard
CSS-030Retailer Warning

The package document declares media overlays styling class names bu...

The package document declares media overlays styling class names but no CSS was found in the content document.

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PreFlight checks for CSS-030 issues in memory and provides 1-click remediation during client-side packaging.

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What This Error Means in Plain English

EPUBCheck detected The package document declares media overlays styling class names but no CSS was found in the content document.. Digital reading systems and bookstores require standard conformance to ensure compatibility across all reading apps.

Why Retailers & EAA Regulations Block This File

Automated book distributors (Apple Books, Amazon KDP, Kobo, and IngramSpark) run strict EPUBCheck validation on ingest and reject non-compliant files.

Technical Specification: W3C EPUBCheck rule CSS-030: The package document declares media overlays styling class names but no CSS was found in the content document.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule CSS-030 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the CSS-030 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.