1. AFAIK, Word does not implement CSS. Period. See
   (a) A Global StyleSheet in Microsoft Word? and
   (b) How styles in Microsoft Word cascade by Shauna Kelly.
2. Converted files (including pdf > Word) are a formatting nightmare. No conversion process creates anything like an optimal Word document.

When I have a document on which I need to do much editing and it is in another format, I import the text only. Then I apply formatting to that document using Styles with a minimum of manual page breaks and/or section breaks. I refer to the original to match appearance.



If you implement cascading styles as set forth in Shauna Kelly's article and then apply them to the text in your document, you may have better success in the export.