PR #4383 inlined custom `@font-face` rules at the very front of the iframe
stylesheet, ahead of the `@namespace epub` declaration that lived inside
`getPageLayoutStyles`. Per the CSS spec a `@namespace` rule is only honored
when it precedes every style and `@font-face` rule; a misplaced one is
silently ignored. That dropped the namespaced
`aside[epub|type~="footnote"]` hide rule, so EPUBs whose footnote `<aside>`
carries a `border: 3px #333 double` rendered a stray horizontal line below
the annotation marker — but only for users who had custom fonts loaded
(otherwise `customFontFaces` is empty and `@namespace` stayed first).
Hoist the `@namespace` declaration to the very start of the assembled
stylesheet, before the inlined custom `@font-face` rules, and drop it from
`getPageLayoutStyles`. Custom faces still precede the `--serif`/`--sans-serif`
font lists that reference them, preserving #4383's first-paint behavior.
Verified in Chromium against the reported book's CSS: the aside goes from
`display: block` (3px double border visible) back to `display: none`.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Huang Xin
d6e981e568