tweaking the Sass per scss-lint rules

Per https://github.com/causes/scss-lint (but alas, it is Ruby and i cant find a libsass version that is Node compatible), so this is an optional local, dev thing if you want to use it.

Also tried my hand at converting hardcoded color values into variables.

Comments inline below.

r= @nchapman
My example sucked. I was thinking we should maybe create variables for things like:
```
$modal-button-hover-background-color
$modal-button-active-background-color
```

etc. But, I think that's overkill for now. Let's move forward with this!