It is recommended that explicit font families only be used to achieve an intended effect, such as conveying that a note is handwritten.
Take into account that users have control over font face, font size, and justification in flowing books. Test your book to make sure it works in most, if not all, cases.
Font sizes should be defined in em or px, not by name (for example, x-small, small, medium, large).
To ensure ideal readability and font scaling, the main text of a book should either not have a defined font-size or should have a font-size of 1em.
Check the font hinting and metrics on embedded fonts to avoid layout problems. Be sure to test them to avoid layout issues and cropped text.
OpenType, TrueType, and SVG embedded fonts are supported.
SVG text should be reserved for use of irregular text paths.
Embedded fonts must be declared in the OPF and CSS.
Font licensing should be verified before embedding fonts.
Make sure that fonts included within the content adhere to accessibility guidelines. See Accessibility for information.