Milla is right. Eid, the actual religious holiday, starts on December 20. There is a national holiday on the 18th, so some companies may choose to give you the 19th off as well.

I would expect that most companies will give, as a minimum, Tuesday December 18 and Thursday December 20.

More generous companies may give Wednesday December 19.

In the case of VERY generous companies, or the government etc, you may also get some days off in the week commencing Sunday December 23, but I wouldn't count on it.