CSS-007 is reported as info by default. Informative only. It does not make the EPUB invalid.

EPUBCheck · Stylesheets

`CSS-007`

Updated: Nov 3, 2026

EPUBCheck CSS-007 is an info message: “Font-face reference "…" refers to non-standard font type "…".” An @font-face rule points to a font in a format EPUB does not list as a core font type.

The official message

Font-face reference "%1$s" refers to non-standard font type "%2$s".

Default severity: Info. Informative only. It does not make the EPUB invalid.
EPUBCheck version: 5.4.0

%1$s, %2$s… are filled in with the file, value or element EPUBCheck found.

Typical causes

Fonts in formats other than TrueType, OpenType, WOFF or WOFF2.

How to fix it

Convert the font to WOFF2, WOFF, OpenType or TrueType, or remove the @font-face rule.

Terms used here

Other CSS messages

CSS-006 CSS selector specifies fixed position.
CSS-008 An error occurred while parsing the CSS: ….
CSS-004 CSS documents must be encoded in UTF-8, detected …;
CSS-003 CSS document is encoded in UTF-16. It should be encoded in UTF-8 instead.
CSS-002 Empty or NULL reference found.
CSS-001 The "…" property must not be included in an EPUB Style Sheet.

Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EPUBLab.