JSFiddle - React, Tailwind, and code Playground

HTML

<div class="info-panel">
    Testing
</div>

CSS

.info-panel {
    	display: block;
    	position: relative;
    	background: #FFFFFF;
    	padding: 15px;
    	border:1px solid #DDDDDD;
    	margin-top:20px;
    }
    .info-panel:before {
    	border:1px solid #DDDDDD;
    }
    .info-panel:after {
    	content: '';
    	display: block;  
    	position: absolute;
    	left: 20px;
    	bottom: 100%;
    	width: 0;
    	height: 0;
    	border-bottom: 10px solid green;
    	border-top: 10px solid transparent;
    	border-left: 10px solid transparent;
    	border-right: 10px solid transparent;
    }
    .info-panel:after {
    	border-bottom-color: #FFFFFF;
    }