JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
   <li style='z-index:1;'>e1</li>
        <div style='z-index:8;'>div</div>
   <li style='z-index:2;'>e2</li>
   <li style='z-index:3;'>e3</li>
   <li style='z-index:4;'>e4gdfgf</li>
   <li style='z-index:5;'>e5</li>
<ul>

JavaScript

var things = $("li").filter(function() {
  return $(this).css('z-index') == '4';
});
alert(things.length)