I am confused? What do you mean by a "Sigil archive". Are you using this to indicate an epub produced by Sigil? And if so, is it an epub2 or an epub3? Epub3 basically follows the css3 standard but much of css3 is not supported in epub2 only readers.
I agree with Turtle91. You should validate the existing css against the proper css specification (css 2.0 or css 2.1 for epub2; and css3 for epub3) and of course follow that up with epubcheck.
|