JSFiddle - React, Tailwind, and code Playground

HTML

<a href="//example.org" typeof="mw:ExtLink"></a>
<a href="//example.org" typeof="mw:ExtLink"></a>
<a href="./House_(TV_series)" typeof="mw:WikiLink">House M.D.</a>
<a href="//example.org" typeof="mw:ExtLink">Example</a>
<a href="//example.org" typeof="mw:ExtLink"></a>

CSS

body {
    color: red;
    counter-reset: numberedlink;
}

a[typeof~="mw:ExtLink"]:empty:before {
    content: "[" counter(numberedlink) "]";
    counter-increment: numberedlink;
}