Added required initial values, fixed invalid syntaxes

[ahnlak]

Slightly-invalid property values tidied up, which fixes lightningcss errors, and addresses both #163 and #132

Two related but distinct changes:

• a few properties were using invalid syntax values (ratio, line-style, content-position) - these now have valid value lists (apart from ratio, which ends up needing to be *

• valid initial-value values provided for all properties that need it (which is most of them)

[ahnlak]

(please ignore for the moment; further testing has thrown up some broken stuff...)

[ahnlak]

Ok, it's a better state now - apologies for the false start, one of those "just because it compiles doesn't mean it works" moments.

A couple of these properties have no rational initial value - which is presumably why they were set to null in the first place; however, because they had non-universal syntaxes set, they were never applied anyway. The offending properties have now been set to a syntax of "*" which, although it feels wrong, reflects the fact that there is no rational initial-value to be set.

While this is functionally neutral, it means that anyone using lightningcss (such as Astro 7 users) will actually be able to compile their projects.

It does feel slightly ugly, so I understand if you'd rather not have this in your codebase and I'll just keep my fork sync'd :-)