Computer Science theory is a form of mathematics. That's how CS got started. It has evolved into something separate from mathematics - certainly related, but also clearly independent.
I've said this before on HN, but there is more to computer science than the math-heavy, CS theory that many people here seem to think is the entirety of computer science. Computer science also encompasses the study of programming language design and implementation, computer architecture, operating systems, networking, graphics and other fields. While math is a part of these fields, math is also a part of organic chemistry.
Perhaps the most fundamental nugget of computer science is that it is everything concerned with computation in both the abstract and in implementation. All of the fields I mentioned stem from that idea, including CS theory.
I've said this before on HN, but there is more to computer science than the math-heavy, CS theory that many people here seem to think is the entirety of computer science. Computer science also encompasses the study of programming language design and implementation, computer architecture, operating systems, networking, graphics and other fields. While math is a part of these fields, math is also a part of organic chemistry.
Perhaps the most fundamental nugget of computer science is that it is everything concerned with computation in both the abstract and in implementation. All of the fields I mentioned stem from that idea, including CS theory.