How does this CSS produce a circle?

Question

This is the CSS:

div {
    width: 0;
    height: 0;
    border: 180px solid red;
    border-radius: 180px;
}

How does it produce the circle

Answer 1

I think that it initially creates rectangle with height and width = 180px and then make curve with given radius like 30px with each corner. So it sets border with given radius.