5
I made my first theme, the xdef theme, a few weeks ago, granted its not the best theme but i was chuffed with what i had learned in making themes.
The way i learned the CSS was with basically looking at other themes CSS files, i also had alocal test site open in xampp, then i just edited the CSS and refreshed the test site to see what changed and I learned what most of the CSS things where for in relation to the theme eg. even and odd classes, etc.
A good place to goto to kearn abit about CSS is the w3schools site
http://www.w3schools.com/css/default.asp
Michael Jackson = King Of Pop
Xoops = King Of CMS