<blockquote>I can not see how to edit css in the theme.</blockquote>
You can edit css for any specific file in ::
template >> ja_portfolio >> css >> any file through ftp client like filezilla, cute ftp
<blockquote>my index file is only 2 kb and there is nothing important to edit there.</blockquote>
The template is powered by T3 framework so most of files can be located in this folder::
plugins/system/jat3/base-themes
For css edits like changing background, font-size e.t.c, You can do the the edits in css files located in css folder of specific template
Introduction and working of T3 Framework::
http://wiki.joomlart.com/wiki/JA_T3_Framework_2/Guides
Please go through above wiki briefly to know more about power of specific framework as you can do many edits through template parameters itself 🙂