You have instructions on docs and several examples here.
Fonts are installed on client machines, so if you add non standar fonts to the list and someone doesn't have the font installed he won't be able to see them.

Example:
$deffonts=array('Tahoma'=>'Tahoma','Georgia'=>'Georgia','Trebuchet MS'=>'Trebuchet MS');


I don't recomend you to use non standar fonts cause I think you can't install them in every client machine who visits your site.

I'll try to explain.

Once you have submitted an article or something like this, the XOOPS system applies your css theme file.
This css controls the whole system appearance (colors, font styles e.t.c).

The css attach function is only to see a real preview of the content before submitting it. It doesn't attach anything fisically 'cause it will happen automatically once the content is submitted.

You are trying to change the font what you see while you're writing with koivi. But it isn't a real font, the font what you see is selected by the browser and it doesn't affect the code.

Once the content is submitted, your css file will be applied, overriding the default browser font.

For example, under Internet Explorer, the default font it's like Times New Roman, under linux it's different.

It's like form buttons, if you see a html form and you're under Windows XP the buttons will appear different than under Windows 98.

Other example, now I'm writing this post and the font that I see is "Times New Roman".
But when I submit it, it appears with "Verdana" style.
Why?
Because the XOOPS css theme file specifies that forum posts will have verdana font.

So, if in your CSS theme file you specify some kind rule which controls the font, for example:

body
{
font:10px Verdana;
}

You will see your published article with Verdana and size 10px.

If you don't control this, the browser will apply it's default font (in case of Internet Explorer, Times New Roman).

Yes, you must update your system_imagemanager.html template with the one you find inside koivi folder.

I've uploaded the last XOOPS editor framework version here.
http://dev.xoops.org/modules/xfmod/project/showfiles.php?group_id=1155

I dont have permissions to upload in the xoopseditor framework project.
You can download from here:
http://dev.xoops.org/modules/xfmod/project/showfiles.php?group_id=1155

@studioc

I'm really interested, Can you send me a link to the theme forge?

I've already finished the tableless newbb_index.html template.
I saved a lot of html tags with it.

The following templates are so complex and need a lot of work:
newbb_viewtopic_flat.html
newbb_viewtopic_thread.html
newbb_thread.html

Here you can find a tutorial to implement koivi in all forms.
https://xoops.org/modules/newbb/viewtopic.php?topic_id=31122&forum=15

If you need help after reading this I'll try to help you.

I'll try to update the editor framework.

Many users on my site said me that newbb2 is too slow loading under internet explorer.

Because of that I'm trying to make a tableless templateset.
(only div's and css). I have finish only the viewforum template, and the next one will be newbb_thread.html

Take a look here, with this template is more confortable for me to visit the forum with my small pda screen.
And I think is faster.

http://www.forjandoleyendas.com/public/fl/modules/newbb/viewforum.php?forum=1

@davidlt

You have here a demo site:
http://www.forjandoleyendas.com/public/testsite/modules/news/submit.php

Now i'm testing contextual menus and solving some minor problems.