CSS defined three global values: initial, inherit and unset
The values are valid for the top level of a property, grammar, but not elements of composed properties:
Note: This implies that, in general, combining these keywords with other component values in the same declaration results in an invalid declaration.
Currently some of the property definitions contain initial and inherit values, but this is not complete and unset is completely uncovered. Instead on relying on the individual property definitions, the values should be handled for all property definitions uniformly.