I appreciate your support.
@JimmyR, thank you, the quick fix has changed one thing.
The default font is more pleasant (azw3 convertion), but it has no effect over Kindle's checkboxes.
Only one default font.
The faulty book :
Css references to font-family : Times.
There is no embedded font in the epub.
(Another book with checkboxes working fine has no embedded font).
Pinch n zoom is ok.
The good book :
Another book from the same serie, has embedded font, and checkboxes are active. I see an extra checkbox Publisher Font. Probably because a TTF font is embedded.
A close CSS code comparison, between two books, may show what the faulty line is. Hard work to crack the conumdrum.
https://mademers.com/the-conumdrum-t...font-handling/
@Brett, your manage tool is a way to explore. Thank you. First I'd like to find the code that inhibates the internal checkboxes.
Best regards