Thank you both for your advices. I had initially a complete svg image with a png inside, but I scrapped it because it was huge and did not display properly. But there may probably have been mistakes on my side.
I am not sure if the use of a background image is such a great idea. The display is very rigid.
I am also trying another idea, putting together the two images within the same container and using a negative margin to make them fit together. It displays nicely on the Calibre editor but poorly on an EPUB. I began with the svg on top of the png, and tried also the other way (png on top), using the property:
Code:
background-color:transparent
.
Anyway, I will follow on trying.