[DiapDealer]

And for what it's worth, the QtWebEngine Preview used by both Sigil and PageEdit renders the the above "Twisty" css-only animation example just fine (with the Qt5.12.3 packaged with the Windows and Mac installers for Sigil 0.9.15+, anyway). But as mentioned earlier, Sigil doesn't have anything to do whether or not the animation will be supported on any particular ereader or epub rendering system. It all depends on their conformance to/interpretation of epub/html/css specs.

Also, there is no need to "export" epubs from Sigil. Sigil has long had the ability to create, edit, and save EPUBS (both EPUB2 and EPUB3). So the notion of "exporting" an epub from Sigil is a bit misleading and/or confusing. The working version IS the final product. Sigil doesn't use an intermediate, proprietary format (like Gimp) that needs to be exported as an epub when ready. And there is no compilation/conversion like with creating a Kindlebook. The markup you write is the markup in the epub. It's just a zipfile with rules (and a different file extension).