Comment 7 for bug 1932392

Interesting MOBI historically never supported percentages for margin
values, only plain numbers. Presumably amazon changed their renderer to
add support at some point.

I'm afraid I am not interested in changing the calibre mobi output
plugin to use percentages, it's a large and invasive change that could
well break other things in what is an extremely stable and legacy
format. I will however special case handling of percentages in margins
to use the standard kindle profile rather than the user selected one.