JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="ui-tabs-panel">
    <li>column 1</li>
    <li>column 2</li>
    <li>column 3</li>
</ul>
<ul class="ui-tabs-panel">
    <li>column 1</li>
    <li>column 2</li>
    <li>column 3</li>
</ul>

JavaScript

$(function() {
    $('ul.ui-tabs-panel').each(function() {         // Get al ULs with .ui-tabs-panel
        $(this).find("li").each(function(i) {        // Go through each LI of this UL
              
            $(this).addClass('col-' + (i+1));  // Add the right class

        });
    });  
    alert($("body").html());       
});