(Warning: This post is techie. It’s also only relevant to you if you want to use Scrivener to create Kindle-ready MOBI files ready for upload to KDP. If you do not meet this description, here is a link to a page of amusing animal GIFs instead.)
Sharing this in case anyone else hits the same problem.
I’ve been periodically using Scrivener to compile ASCENSION POINT into MOBI format, to see how it looks on my Kindle. I’ve also been using the Kindle Previewer, which cleverly emulates different types of Kindle (DX, Fire, iPhone, etc), and happily my book always looked great.
That is, until lovely fiancée came back from D.C. with a brand new Kindle Fire for realsies.

I threw the latest draft of ASCENSION POINT on there, and discovered that all the bold text was, well, not. Not-bold. Unbold?
Anyway.
I fired off an email to Kindle Support, who asked me for a sample MOBI. They took a look at it and declared that:
“We have looked over your content – to make the content bold, you are using the CSS style “font-weight:600”. Please change this style to “font-weight:bold”. This is the recommended CSS style to make the content bold.”
Who knew? The lovely tech support folks on the Scrivener forums couldn’t think of a way to make Scrivener use a different CSS style (though they are going to look into it) but they did share a cunning workaround, which I here reproduce:
- Compile to ePub instead.
- Open ePub in Sigil.
- Switch to ‘Code View’.
- Do a Find/Replace of ‘font-weight:600’ to ‘font-weight:bold’ in ‘All HTML Files’.
- Save the ePub, and close Sigil.
- Run Kindle Previewer, and open the ePub.
- Kindle Previewer automagically creates a MOBI from the ePub.
- Ta-da! The problem, it is solved.
It, like all things, is easy when you know how.