Use unitless numbers for line-height values

Use unitless numbers for line-height values

Using <length> type values for line-height can give unexpected
inheritance behaviors. If using <length> values, the inherited
line-height on children is calculated using the font-size of the parent.
What we want is for the line-height of children to be calculated using
it's own font-size.

By instead using a unitless number, we get the behavior we want. Note
that this bug has no effects right now since no children to any of the
related elements have different font-sizes.