JSFiddle - React, Tailwind, and code Playground

HTML

<my-header id="myHeader">I am a header<br/></my-header>

CSS

my-header{
    border:1px solid black;
    height: 100px;
    width: 100%;
    display:block;
}

JavaScript

(function() {
    var div = document.createElement('sub-header');
    div.innerHTML ="I am a sub-header";
    document.getElementById("myHeader").appendChild(div);
    
})()