How to center the center circle?

Question

How to center the center circle (CSS only)?   [Assume latest CSS3 browser support.]

Must maintain v/h centering when parent w/h changes dynamically.

Answer 1

It isn't the perfect solution, but it works for me. The centering tags that SHOULD be used didn't change anything here, so I hope anyone will come with a better solution.

.circle .circle{
    width: 15px;
    height: 15px;
    margin-top: 15%;
}