JSFiddle - React, Tailwind, and code Playground

HTML

<body>       
    <div class="classA"></div>     
</body>

CSS

.classA{
    position:absolute;
    width:25px;
    height: 25px;
    border-radius: 10px;
    background: #f57df5;
}
.classB{
    
    -webkit-transform : rotate(30deg) translatex(120px);
    background-color:black;
}

JavaScript

$(document).ready(function(){
    var x = document.getElementsByClassName('aa');
    x[0].className = "classB";     
});