Do grad schools care about non major related classes?

Yes, they care. They might be slightly less interested in a "B" in a science course than in your grades in Humanities courses, or vice-versa, but your overall performance matters, because it is an indication of your general intelligence and ability.

And any courses outside of your major that might have a tangential relationship will matter, too. In my field, Art History, literature and history courses matter. In my case, it helped that I did very well in science and social science courses, because they told the graduate departments to which I'd applied that I was both a hard worker and someone with an analytical mind, and that matters in graduate programs, no matter what they are.

Do the very best you can in ALL your courses. Faculty in graduate programs won't be thrilled by mediocre grades in courses outside of your major unless you are so utterly, spectacularly, brilliant in your major courses that they think you're a future Nobel Prize or Pulitzer Prize or Booker Prize winner in that single, specific field.

Most of us have never demonstrated such unusual and narrow brilliance as undergraduates.

yes and no.

They care MORE about major related classes, but they will evaluate your whole transcript. If you are a history major, for example, and you got a 4.0 in every history class but got a 2.0 in algebra, the school probably wouldn't care that much. Of course if your a 4.0 history major but 2.0 every other class they might be skeptical.