I danced ballet for over 10 years, and my legs are slightly athletic, but not to a bulky extent, and much of it is generic in the first place. I've always had defined legs, even when I was a little, little kid

But if you look at professional dancers, there legs are very, very defined and very, very sleek.
If you use the correct muscles when using ballet steps to tone and define, you're legs will be sleeker. That means using your hamstrings and inner thighs and trying to relax your outter thighs. It's quite a difficult concept, but if you're not careful, and grip your quads, you'll bulk. If you are going to try this, make sure to focus on using your inner thighs, primarily.