Great! I've modified both the template file and the stylesheet with these results.
I'm keeping a copy of the files in the folder.
I'm sharing a zip file in case anyone needs it.
Code:
README.txt
==========
Calibre Book Jacket Customization
---------------------------------
This package contains two modified files:
- template.xhtml
- stylesheet.css
These files control the structure and style of the "Book Jacket" that Calibre inserts into books during conversion.
Installation paths (requires administrator/root privileges):
- Windows:
C:\Program Files\Calibre2\resources\jacket\
(on some installations: C:\Program Files\Calibre\resources\jacket\)
- macOS:
/Applications/calibre.app/Contents/Resources/jacket/
- Linux:
/usr/lib/calibre/resources/jacket/
(depending on distribution: /opt/calibre/resources/jacket/)
⚠️ Warning:
- Always back up the original files before replacing them.
- Keep that backup in a safe place (for example, this ZIP).
- A Calibre update may overwrite these files. If that happens, simply copy your customized versions back from the backup.