See this related earlier thread.
https://www.mobileread.com/forums/sh...d.php?t=354137
Note, there are bugs in ADE and now Thorium about using 100% that means a bit a trial and error will be needed to get this to work on most platforms.
Another possible solution is to leave the 100% for height and width but instead add height="98vh" to the parent div style so that it will constrain the vertical height of the svg element to fit on one page vertically.
And ..,
If you are editing an epub2, and want to update it to epub3, you can use the ePub3itizer plugin in Sigil.