JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

body {
  margin: 0;
}

.container {
  margin: 2rem;
  border-right: solid 1px gray;
  position: relative;
  height: 200px;
  width: 0;
}

.box {
  content: "";
  background: white;
  height: 2rem;
  width: 2rem;
  border-top: solid 1px gray;
  border-right: solid 1px gray;
  position: absolute;
  top: 50%;
  left: 0;
  margin-left: -1rem;
  transform: rotate(45deg);
  margin-top: -1rem;
}