JSFiddle - React, Tailwind, and code Playground

HTML

<br />
<div class="container">
Test Container
</div>

CSS

.container {
    margin-left: 15px;
    width: 200px;
    background: #FFFFFF;
    border: 1px solid #CAD5E0;
    padding: 4px;
    position: relative;
    min-height: 200px;
}

.container:after {
content: '';
display: block;
position: absolute;
top: 10px;
right:-7px;
width: 10px;
height: 10px; 
    background: #FFFFFF;
    border-right:1px solid #CAD5E0;
    border-bottom:1px solid #CAD5E0;
 -moz-transform:rotate(-45deg);
  -webkit-transform:rotate(-45deg);
}