[css-inline-3] Add keywords for raised / dropped initials #2955

In #2950 (comment) @AmeliaBR wrote:

@Crissov, I'm not sure if the specific numbers you suggest are common enough to make default. But, I do like the idea of keywords dropped and raised for the two most common use-cases for the second property. (I personally find it confusing that you need to specify a "drop" of 1 for not-dropped-at-all.)

[property-name]: 3 dropped;
[property-name]: 2 raised;

dropped would still be the default, and any other levels of sunken-ness could still be set with integer values.

This is maybe a separate issue, though.

//CC @Dan503

It would be pretty easy to add keywords that compute through to an integer, with dropped copying the first value and raised computing to 1.