Thanks for this code
but I still don't know whether this goes to the css file or maybe that other file with opf extension or elsewhere.
Besides is this standard code or code specific to one ebook. After all one cannot just take the css of one book and copy paste it to another's.
If book publishers and e-readers brands did their job we wouldn't have to bother messing with the code.
Code:
<div>
<svg xmlns="http://www.w3.org/2000/svg" height="100%" preserveAspectRatio="xMidYMid meet" version="1.1" viewBox="0 0 296 475" width="100%" xmlns:xlink="http://www.w3.org/1999/xlink">
<image height="475" width="296" xlink:href="../Images/cover.jpeg"></image>
</svg>
</div>