African Storybook (ePub) layout issue

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Summary

I just updated our African Storybook channel with the new ePub versions of the files (as opposed to what I remember was an HTML5 file before). They load beautifully, even on our older iPad2s which had a good deal of trouble with the other version. However, they don’t present in an optimal way. I have attached a screen shot of what I’m seeing across devices.

You will see that the picture and text show up on the same “page” to the left side of what would normally be a 2-page spread in landscape orientation, which is how they show up on the African Storybook web site online reader (2nd picture attached as illustration). When viewing these books on a tablet, turning it to portrait orientation would normally result in the picture and text filling up the screen, but instead the picture and text shrink down to occupy a relatively equal portion of the page with a similarly equal portion of unused white space.

Kolibri example:

African Storybook example:

Technical details

Version: 0.15.8
OS: Linux-5.15.76-v8±aarch64-with-glibc2.31
Python: 3.9.2
Installer: deb kolibri-server - 0.4.0-0ubuntu2
Server: nginx/1.18.0
Database: /home/pi/.kolibri/db.sqlite3
Free disk space: 696 GB
Server time: Fri Dec 16 2022 16:10:49 GMT+0100 (West Africa Standard Time)
Server timezone: Africa/Douala
Device ID: 86a460380dbbc8ff95b31688d3694024

Browser: Safari, Chrome