class="mb-1 w-2 mt-3" style="border-top: 2px solid #ff0048; border-radius: 100%;" code example

Example: border-radius circle using %

.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>