Andre, it may be 3 variants might work for you but you are then placing the scaling of your work on the smartphone/browser and ultimately the viewer as a responsive approach is really only tuned for the widths you chose.
You are not simply a user of the product, you are a designer using a tool. Every tool has its quirks and faults. A sprinkling of CSS should be seen as a Widget and I could have presented it as a black-box without explanation. I don't see challenges for things like ECWID, where it has a genuine Xara/ECWID fail across Variants.
I think my 'widget' works and those who need it are free to use. What pleased me is there are few pure CSS solutions around on the Web, most seem to use JavaScript or jQuery, both with their own issues.
Further, Xara in delivering its new Modular Websites, seems to have gone partway into accommodating the flashing around StFW by setting up Fade Ins for most of its Web Blocks. rather than use my CSS approach, you might try selecting everything on the page (without current Web Animations) and using Reveal > Fad in instead. No CSS, just Xara's in-built JavaScript functions.
Workarounds are a designer's privilege and Xara's technical backlog.
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