JSFiddle - React, Tailwind, and code Playground

HTML

<p>some text</p>

<p>some text</p>

<h1>A H1 TITLE</h1>
<p>some text</p>
<p>some text</p>
<p>some text</p>
<p>some text</p>

<h1>A H1 TITLE</h1>
<p>some text</p>
<p>some text</p>
<p>some text</p>
<p>some text</p>

    <h2>A H2 TITLE</h2>
    <p>some text</p>
    <p>some text</p>
    <p>some text</p>
    <p>some text</p>

<h1>A H1 TITLE</h1>
<p>some text</p>
<p>some text</p>
<p>some text</p>
<p>some text</p>

<div>
  <p>some text</p>
</div>

<p>some text</p>

CSS

.special_p{color:red}

JavaScript

$("h1").nextUntil(":not(p)").addClass("special_p");