deeper GenPress CSS3 learning

hi guys,

i’m studying WordPress (zac gordon), learning tons ??

getting much more familiar & comfortable w templates and PHP in general.

can you plz recommend a good book or online tutorial for CSS3 (variables, etc)?

i’d like to become more proficient and confident, esp w variables and functions (as a way to better understand GenPress also ??

thank you for making the web even more awesome! Lester