css border circle code example

Example 1: css circle

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

Example 2: css circle border

.circle {
    background-color:#fff;
    border:1px solid red;    
    height:100px;
    border-radius:50%;
    -moz-border-radius:50%;
    -webkit-border-radius:50%;
    width:100px;
}
<div class="circle"></div>