JSFiddle - React, Tailwind, and code Playground

HTML

<fieldset>
<legend>border</legend>
</fieldset>

CSS

body{
  background:#333;
}
div{
  width:300px;
  height:200px;
}
fieldset{
  display:inline-block;
  background:#444;
  border-radius:10px;
  border-style:solid;
  border-color:#121212;
}