3.3 HTML & CSS

The HTML & CSS tab has some hidden gems. It is fair to say that InDesign does not write a very good ebook CSS file. It exports too much information, including things that will definitely interfere with accessibility. 

For example, the InDesign generated CSS will define the text as black, which will mean that most text will not invert when a user switches to night mode. Defining the body font size as 0.917em — which is often what 12-point type turns into — means that a user with low vision may not be able to upsize the font in some reading systems. Some of the CSS is nonsense that no reading system will respect, and some of it is repetitive and unnecessary — like text-transform:none. Twenty lines of CSS definitions can be condensed down to eight lines. With a really good CSS, it could be compressed even further. 

InDesign’s CSS is not only overburdened but can actually get in the way of accessibility. We encourage you to develop your own CSS, or crib from others. Blitz.css is a very good starting place. While no longer under active development, Blitz CSS is still a very usable, excellent ebook CSS resource. Please consider starting there and swapping in that set of CSS definitions for the overwrought CSS that InDesign will produce for you. To do that, uncheck Generate CSS in this window, and ask InDesign to embed CSS that you add here in the Additional CSS window. The ability to change the font size and font are foundational to accessibility so don’t let InDesign’s CSS to undo the good work you’ve done to make an accessible EPUB.

The final window is the metadata window — and it is already populated with the details that you may have put into the File —> File Info window. You might add an ISBN identifier here, and a publisher to round out this data.