I've seen this sentence here. Shouldn't it be "your Christmas fashion"? If it's right, what does it mean?
For anything written or said, in any kind of advertising, including all TV, movies, and music,
There are no hard and fast grammar or pronunciation rules.
This is because the point of entertainment is to draw your attention to the advertising, and a good way for advertisers to do this is to violate some kind of rule they think you expect them to follow.
Consequently, if you think you see a mistake on TV or in a movie, pay no attention to it.
It's being done on purpose, and your best strategy is to ignore it -- it's just more advertising.
A "family Christmas" is a Christmas spent with ones family. (e.g. How to survive family Christmas)
They are potentially trying to imply that shopping for fashion during Christmas is another strand of a well balanced Christmas.
It seems to me to depend on which word you deem the noun (subject or object) and which you deem the adjective.
If one talks of a family Christmas, a religious Christmas, an over-indulgent Christmas, sporting Christmas, then Christmas is clearly the noun that the other words (adjectives) are describing, and fashion Christmas seems to fit with them.
However considering that one could talk of Spring fashion, Easter fashion, Parisian fashion, Beach fashion etc., then among them Christmas fashion would be in order, with fashion a noun qualified by the adjective Christmas.
In English, one way to build a nominal is to string a bunch of nouns together (see Chapter 12 of Jurafsky and Martin's Speech and Language Processing). Here are some examples of nominals built in this way.
Mineta staggered to a stall and threw up, splurting the remains of a hotel breakfast into the toilet bowl. Milk tea, orange juice, and a blueberry muffin. Her briefcase had burst open, spilling trial transcripts and evidence bags across the courthouse bathroom floor. This was shaping up to be a hell of a family Christmas.
The ad copy you noticed is another example of this construction. As Martin Smith points out, just as a "family Christmas" is a Christmas celebration centered around family, a "fashion Christmas" suggests a Christmas celebration centered around fashion.