JSFiddle - React, Tailwind, and code Playground

by Ayri Rin

HTML

<div class="block"></div>

CSS

.block {
    border: 1px solid green;
    border-radius: 10px;
    padding: 20px;
    position: relative;
   }
   .block::before, .block::after {
    content: ''; 
    position: absolute;
    left: 20px; 
    top: -20px;
    border: 10px solid transparent;
    border-bottom: 10px solid green;
   }
   .block::after {
    border-bottom: 10px solid white;
    top: -19px; 
   }