JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="test">
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li class="active">4</li>
    <li>5</li>
</ul>

CSS

.active_slide{
    color: green;
}
.active{
    color: red;
}

JavaScript

for(
    var a = document.querySelector("#test"), 
    b = [].indexOf.call(a.children, a.querySelector(".active"))-1;b>=0;b--
){
    a.children[b].className = "active_slide";    
}