What is the problem?
I think the problem is it has two nested <div class="mw-parser-output">, which means font-size: 0.875em is applied twice.
I wonder if this bug affects other extensions or features?
Steps to reproduce problem
- Go to https://pl.wikisource.org/w/index.php?title=Page:Wac%C5%82aw_Niezabitowski_-_Ostatni_na_ziemi.djvu/66&action=edit
- Click "Pokaż podgląd"
- Look at the font size of the preview text
Expected behavior: It should be 14px (if your browser is at 100% zoom and 16px default font size)
Observed behavior: It is 12.25px
You can also reproduce this on beta, e.g. https://en.wikisource.beta.wmflabs.org/w/index.php?title=Page:War_and_Peace.djvu/30&action=edit