Is 30 days including holidays like Christmas, New Years Eve/Day, etc? Or is 30 days in addition to mandated holdiays?

Most people in the US have 2 tiers of vacation days: mandatory holidays (I'd say between 8-14 mandatory holidays is pretty standard at tech companies) plus an additional 3-4 weeks (15-20 days).

For most engineers in the US, something like 10 holidays + 3 additional weeks (or more) can be expected for a minimum total of 25 days. Plus 3-5 "sick/personal" days brings you up to roughly 30 days.