It's both, Nazism is more nationalism than social class though.

How was it about class?

... The Holocaust?

Again, that was all about nationalism, and, to a certain extent, social conservatism, not class. They didn't want Jews to occupy a lesser place in Germany than what they considered true Germans, they wanted them out of there. That's why they tried to get them all to emigrate before the war.

A "master race" is social class. It wasn't just Jews, it was all non-Aryans who were sub-leveled. It's so obvious, I don't know why you're arguing this.