For example: if you are using beez_20 template, then your css file will be saved here: www.yoursite.com/templates/beez_20/css/com_koparent/koparent.css

If you do not want to use online editor but you want to edit those files manually, you can just copy those files to your template folder.

Getting a head-start with manual editing the css files

If you are new to Joomla! development, then it is probably easiest to start with the koparent.css file, and try modifying it to get what you want. To do this, you should make a copy of the existing css file in the css directory of your template, and then modify the copy.

The directory structure you need is:

TEMPLATE_NAME/css/com_koparent/FILE_NAME.php

For example, if you want to change the 'koparent.css', then you should copy the file at

PATH_TO_JOOMLA/media/com_koparent/css/koparent.css
to
TEMPLATE_NAME/css/com_koparent/koparent.css

(note the slight difference in directory structure)

There you can see how simple modifications can make big impact on the site and how it is easily changed. Note: When you are making modifications in your template folder you do not have to worry about upgrading Koparent extension, it will never override your modifications in template folder.

Further tips

For the FireFox web browser, an extension called Firebug is available, which is useful for browsing a page's HTML source and matching it up with the PHP code used in template overrides. Now firebug is also available for IE called Firebug Lite.