Cannot adjust line-height using Extra CSS

[Waylander]

I am trying to adjust the line-height of an AZW3 ebook using the Extra CSS function in Calibre. The CSS looks like this:

body
{
orphans: 0; widows: 0;
line-height: 1.3em
}
html {
margin-right: -41px;
margin-left: -41px;
break-inside: avoid !important;
}

This works on my Paperwhite running fw 5.17.x. But No matter what em I set the line height, it makes no difference on my Paperwhite. Is this because it's running fw 5.20.1, and doesn't show my line-height value? I've tried bigger and smaller em with no change, have unticked the fonts and padding options from 'Filter Style Information', and have set minimum line height and line height to 0.0 in the Fonts section of the conversion window. I don't what's going on or how to rectify it.