JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="header">TITLE</div><div class="corner"><div></div></div>
   <div class="body">Content</div>
</div>

CSS

.container{
    width: 660px;
    background: #fff;
    color:white;
}
.container .header{
    float: left;
     width: 110px;
    background: #333;
    border-radius: 5px 5px 0 0;
}
.container .body{
    clear: left; 
    width: 660px; 
    background: #333; 
    border-radius: 0 0 5px 5px;
}
.corner{
    display:inline-block;
    width:15px;
    height:15px;
    position:relative;
    bottom:-4px;
    background:#333;
}
.corner>div{
    height:inherit;
    width:inherit;
    background:white;
    border-radius: 0 0 0 5px;
}