An excellent CSS reference and learning tool
Figuring out the Zen Cart stylesheet while learning CSS has always been a large part of the Zen learning curve. I've just come across a site which can help.
Check out CSS Reference at Sitepoint. It's well laid out, easy to navigate to what you want, and simply explains what you need to know. For example, I've spent years doing CSS with only a vague idea about how to work with selectors in combination, but after 30 minutes reading about it in this reference, it's all come clear. I like it a lot!
Breakfast: the most important donut of the day.