Well, the problem is not learning CSS or learning how to program in ruby, but the structure of discourse itself, how its interface is organize, how the tree of display elements work (in order to find the correct name of elements to change css styles), etc.
For learning css and ruby programming there are plenty of sites, although links to good learning sites are always welcome.
Thanks for the links to the guides, I am interested in making basic css adjustments and some basic components and plugins.
Are there similar guides to theme components and plugins?