This is technically responsive, but I think you have a fair criticism. A single rule like this would be much more maintainable:

#content .grid-container {
	width: 90vw;
	min-width: 12rem;
	max-width: 75rem;
	padding: 2rem 0 1rem;
}

Obviously, media rules have their place, but not for something that's consistantly a full width container like this seems to be.