DO NOT MERGE (in #57): SASS diff from stanford themed branch for master

@frrrances & @ormsbee - here are the straggling SASS changes to get the Stanford theming branch into master.

I replaced a few variables with general ones. (btw, going forward we all need to talk about variable naming and stuff...)

I also discovered how lovely SASS mixins truly are, and I think we should use them everywhere to enable nitty gritty theming...