JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box">
  <div></div>
</div>

CSS

.box{
  width: 220px;
  height: 220px;
}

.box div{
  width: 180px;
  height: 180px;
  margin: 2px;
  border: 18px solid purple;
  background-color: black;
  display: flex;
  justify-content: flex-end;
  align-items: center;
}

.box div:after{
  content: "";
  width: 18px;
  height:100px;
  background-color: yellow;
  right: -18px;
  position: relative;
}