Prescribing specific fonts in ebooks can be controversial, but there’s no doubt that it can be important to be able to make some typographic choices without having to embed a font in the ebook file, with the necessary font license, and all the other caveats that brings (such as getting this to work in Apple’s iBooks). One example I use again and again is setting headings and titles to be in a (i.e. any available) sans-serif font. This is a small design decision that can go a long way towards adding a professional touch to an ebook.

However, one problem I have always encountered is that the Kindle Fire mode in Kindle Previewer has never honoured the following CSS:

.heading {
  font-family: sans-serif;
}

This week, I discovered why, thanks to this discussion. For whatever reason (i.e. ignorance of standards), Kindle Fire mode (not having a Kindle Fire myself, I have no idea if this is true for the real device too) requires a specific typeface to be referenced first, thus:

.heading {
  font-family: "Arial", sans-serif;
}

Hey presto, it works. It shouldn’t, but it does. Given that the Kindle Fire only ships with 8 fonts (unless things have changed recently), it’s probably best to choose one of those in your CSS; I experimented with "Trebuchet", which is supposed to be one of the 8 and looks a lot nicer than Arial, but it didn’t work at all, simply rendering as a serif font, as before.