I agree! Doing cardio is great for losing fat, but to get your arms looking good, you will need to lift some light weights or do specific arm exercises, like tricep dips. Try to do exercises with lighter dumbbells that will work all of the arm muscles. Some people JUST do bicep curls, but you definitely should work the sides and backs of the arm too.
I find that cardio usually is enough for my legs (I like to go jogging or use the elliptical), but I also do lunges and leg presses for my legs. You can also stand up and down on your toes to work the calves.