JSFiddle - React, Tailwind, and code Playground

HTML

<table width="100%">
    <tbody>
        <tr>
            <td>col 1</td>
            <td>col 2</td>
            <td>col3</td>
        </tr>
        <tr>
            <td>col 1</td>
            <td>col 2</td>
            <td>col3</td>
        </tr>
        <tr>
            <td>col 1</td>
            <td>col 2</td>
            <td>col3</td>
        </tr>
        <tr>
            <td>col 1</td>
            <td>col 2</td>
            <td>col3</td>
        </tr>
    </tbody>
</table>
<button>Click to apply custom class</button>

CSS

td:first-child { background-color: #ccc; }

/* or see JS */

td.custom-class { background-color: yellow; }

JavaScript

$(function() {
    $('button').on('click', function() {
      $('tr').find('td:first').addClass('custom-class');    
    });
});