Kindle Format 8 (KF8) is Amazon’s next generation file format offering more than 150 new features and enhancements that includes HTML5 and CSS3 support that publishers can use to create all types of books. KF8 powers the book reader Kindle Fire and it replaces the Mobi format. Included in the 150 new formatting capabilities are embedded fonts, drop caps and CSS selectors such as line spacing, alignment, justification, margin, color, style and border. Kindle Direct Publishing supports KF8 so books created using the new Kindle Publishing Guidelines can be published via KDP.
Kindle Fire is the first to support the Kindle Fire 8. Mobi format ebook will still work with e-ink devices and apps though, they just need to be updated. Just read the Kindle Publishing Guidelines to learn the update process.