JSFiddle - React, Tailwind, and code Playground

HTML

<table border="1">
    <tr>
        <td>col1</td>
    </tr>
    <tr>
        <td>col2</td>
    </tr>
    <tr>
        <td>col3</td>
    </tr>
</table>

CSS

table {
    counter-reset: rowNumber;
}

table tr {
    counter-increment: rowNumber;
}

table tr td:first-child::before {
    content: counter(rowNumber);
    min-width: 1em;
    margin-right: 0.5em;