The stylesheet exists as a single place to manage all font sizes. To use
a font size in your stylesheet, follow this procedure:

1. Add a well-named entry to the `$FONT-SIZES` map with the value set to
   the font size for that element.

   No font sizes should ever be declared outside of this map.

2. If you wish to include a `font-size` declaration in your stylesheet,
   `@include font-size()`, passing it the name of the component to retrieve
   the font-size for.

3. Retrieving the actual font-size dimension (for example, to be used in a
   calculation to determine necessary padding) should be done by passing the
   same argument discussed above to the `font-size` *function*.

4. Foo
5. Bar

6. Baz
* Hi