If you dig further down into the packages directory, (from the sounds of it) you should find a package in there for the slate theme, in that a theme folder and then in that the main.css file.

HOWEVER!

A theme that is installed as a package is really meant to be left as is, as packages can be updated (bug fixes and such), meaning that if you make a change to it, it may get overwritten later on.

All the extra folders you've seen aren't redundant, they are used for adding your own components and themes (that aren't in packages) and for overriding things. Once you get your head around it, you'll see that they are all needed.

So back to the theme editing - the best approach is to learn how to take a copy of a theme and install it as a new theme (with a different name). Then you can safely make changes to it. It's pretty quick to do and not complicated.

This guide explains all this and the process:
http://www.concrete5.org/documentation/how-tos/editors/customize-a-...

Take particular note in that guide about the /concrete folder, don't ever edit anything in that.

Hope that helps.
-Ryan

Thanks mesuva,

The workflow you mention is much more inline with what I'm familiar in drupal, just file path structures are different.

I'll definitely read the article you mention. I've still not figured my way around the documentation for c5.