I'm watching philosophy crash course, and the narrator claimed that Utilitarianism is the antithesis of the of Kant's categorical imperative. However, on the surface, I can't see a major difference. How are do the two differ in their approaches?

I'm watching philosophy crash course, and the narrator claimed that Utilitarianism is the antithesis of the of Kant's categorical imperative. However, on the surface, I can't see a major difference. How do the two differ in their approaches?