JSFiddle - React, Tailwind, and code Playground

HTML

<div id="rect">
    <div id="cir">
    </div>
</div>

CSS

#rect {
  width: 500px;
  height: 50px;
  background: green;
  margin: 100px;
}
#cir {
  width:150px;
  height: 150px;
  background: green;
  border-radius: 100%;
  margin: 0 auto;
  position: relative;
  top: -50px;
  }
}