JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box">
   <div class="triangle-topright"></div>
   <h3>title</h3>
   <p>stuff</p>  
</div>

CSS

.box{
    -webkit-border-radius: 6px 6px;
    -moz-border-radius: 6px / 6px;
    -khtml-border-radius: 6px / 6px;
    border-radius: 6px / 6px;
    width:33%;
    border: 1px solid #DDD;
    display: inline-block;
    margin-right:10px;
    margin-bottom: 10px;
    max-width: 290px;
    padding: 10px;
    overflow: hidden;
    margin: 20px;
}

.triangle-topright { 
    width: 0; 
    height: 0; 
    border-top: 50px solid #fafad6; 
    border-left: 50px solid transparent;
    float: right;
    margin-top: -10px;
    margin-right: -10px;
}