That document you link to is a 10-year-old draft, and far from the latest. Now, if you look at the latest revision of the Style Attributes spec, which is a 2010 Candidate Recommendation that covers basically the same inline style declarations that we use every day, you won't find any @import
rules mentioned anywhere anymore.
This means they took it out, presumably because it didn't make sense in retrospect, or it was difficult to implement, or some other reason entirely.
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