JSFiddle - React, Tailwind, and code Playground

HTML

<div class="cont">
  
</div>

SCSS

.cont {
  width: 100px;
  padding: 0 15px;
  margin: 0 auto;
  position: relative;
  background: blue;
  height: 200px;
    
  &:before {
    content: '';
    display: block;
    position: absolute;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    right: -40px;
    top: calc(50% - 25px);
    background: #000;
  }
  
}