No, not really, and given the length of time ereaders stick around, you’re really probably best off assuming the worst. If there’s something complex layout-wise that I want to do then I often use @supports blocks. For example, in a recent book I worked on I had a layout that would be be accomplished with flexbox, but I started with floats instead and overrode that for better ereaders: https://github.com/standardebooks/harry-harrison_planet-of-t...

The tooling does two main things: create a valid epub3 skeleton for your content, and build your book into “compatible”, Kobo and Kindle versions. You need to supply the valid XHTML.

There’s more info on the build process at https://news.ycombinator.com/item?id=46469341