JSFiddle - React, Tailwind, and code Playground

HTML

<div>foo</div>

JavaScript

$.expr.pseudos.icontains = $.expr.createPseudo(function(arg) {
    return function(elem) {
         return (elem.textContent
        || elem.innerText
        || jQuery(elem).text()
        || '')
        .toLowerCase()
        .indexOf(arg.toLowerCase()) >= 0;

    };
});

$("div:icontains('FOO')").css("font-size", "200%");