JSFiddle - React, Tailwind, and code Playground

HTML

<ol>
    <li>Main
        <ul>
            <li>Secondary A</li>
            <li>Secondary B</li>
            <li>Secondary C</li>
        </ul>
    </li>
</ol>

CSS

ol li:before {
    content: counter(li);
    counter-increment: li;
    padding: 0.5em;
}