JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
</div>

CSS

.wrapper {
  width: 500px;
  height: 200px;
  border: 1px solid black;
  border-top: none;
  position: relative;
  overflow: hidden;
  z-index: 1;
}

.wrapper:before {
  content: '';
  position: absolute;
  width: 100%;
  height: 100%;
  border-radius: 80%;
  border: 1px solid black;
  left: 0;
  top: -50%;
  z-index: 2;
}