circle on a circle in css code example

Example 1: css circle

#circle {
      width: 100px;
      height: 100px;
      background: red;
      border-radius: 50%
    }

Example 2: drawing a circle with css

#it is the border-radius:50; that makes the circle.
.MyCircle{
  width:100px;
  height:100px;
  background-color:blue;
  border-radius:50px;
}