JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
  background:blue;
  
  /*
  border-top:10px solid red;
  border-bottom:10px solid red;
  */
  border:10px solid red;
  border-left:1px solid transparent;
  border-right:1px solid transparent;
  
  
  border-top-right-radius:20px 10px;
  border-top-left-radius:20px 10px;
  /*
  border-radius: 20px 20px 0 0;  
  */
    
  height:100px;
}