JSFiddle - React, Tailwind, and code Playground

HTML

<h1 id="header">Welcome to My Website</h1>

CSS

#header{
  max-width: 960px;
  min-height: 100px;
  text-align:center;
  background-color:#000;
  color:#fff;
  line-height:100px;
  position:relative;
}
#header:after{
    content:"";
    border-left: 25px solid transparent;
    border-right: 25px solid transparent;
    border-top: 25px solid #fff;
    position:absolute;
    left:40%;
}