Install yelp-xsl by entering the following commands in the terminal:
sudo apt update sudo apt install yelp-xsl
Description:
XSL stylesheets for the yelp help browser
Yelp-xsl contains XSL stylesheets that are used by the yelp help browser to format Docbook and Mallard documents.
Homepage: https://wiki.gnome.org/Apps/Yelp
Version: 3.20.1-4
Section: gnome