I want to change font and font-size when I add new content on my site in Joomla! administrator.
I don't know how to do it in my version - Joomla! 1.0.12 Stable [ Sunfire ].
I know in the next version of Joomla! I can use the Joomla Content Editor (JSE), but is there any (simple) way to get it in my current version?
Wow! Joomla 1.0 has been unsupported since July 2009 - nearly 7 years ago. Maybe it's time to upgrade?
If there is an option in the editor to switch to HTML mode, you may be able to add in-line styling.
Alternatively, you may be able to edit the template CSS file to achieve a site wide change of body text font and font size (if this is what you want). You should be able to find the appropriate CSS file by looking in the page source.
It looks like you can still download JCE Editor for Joomla 1.0.x but I'm not sure if this applies to version 1.0.12 or not:
https://www.joomlacontenteditor.net/component/zoo/item/component-10x
I suggest running a backup before trying to install it.