JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Title #1</h1>
<p>Text</p>
<p>Text</p>

<h1>Title #2</h1>
<p>Text</p>
<p>Text</p>
<p>Text</p>

<h1>Title #3</h1>
<p>Text</p>

CSS

div { padding: 5px; border: 1px solid blue; margin: 5px; }
h1 { background-color: lightblue; font-size: 1.2em; margin: 0px; padding: 2px; }

JavaScript

$(function () {
    $('h1').each(function () {
        $(this).nextUntil('h1').add(this).wrapAll('<div />');
    });
});