@kylefiedler Two notes:

1. I think it’s a good call to use `$em-base` as the base value for the modular scale function. So the entire `$modular-scale-base` variable could go away in favor of just using that.
2. A strange thing happens when I swap in `em($em-base)` for the `$value`: when globally changing `$em-base` to a smaller number (like 12px instead of the 16px default), everything using the modular scale function get _larger_ instead of smaller. It’s backwards! Quite weird, and I haven’t been able to figure out why yet.

Thoughts?