JSFiddle - React, Tailwind, and code Playground

HTML

<div class="item">
  <div class="border"></div>
</div>

CSS

*{
  margin:0;
  padding:0;
}
.item{
  width:200px;
  height:200px;
  border:1px solid red;
  margin:30px;
  position: relative;
}
.border{
  width:50px;
  height:50px;
  border:1px solid red;
  border-top-color:white;
  border-left-color:white;
  position: absolute;
  top:-1px;
  left:-1px;
  border-bottom-right-radius:50%;
}