how to make circle inside circle css code example

Example 1: making a circle css

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

Example 2: how to create a circle with css

<div id="circle">
</div>

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