How to do something like border-top-left-color CSS

Question

Only border-left-color, border-right-color, border-top-color, and border-bottom-color are offered when I wish to colour a border. Where can I get the proper bottom edge of a circle that I wish to colour?

As I am not very good at describing things, kindly correct me if I am not making any sense.

a single illustration Take note of the sheen and the button on the iPhone's bottom.