JSFiddle - React, Tailwind, and code Playground

HTML

<div class = 'parent'>
    <div class='child'>
        I'm a child div!
    </div>
</div>

CSS

.parent{
    position: absolute;
    width : 300px;
    height : 100px;
    padding : 10px;
    background: red;
}

.child{
    background: blue;
}

JavaScript

var parent = document.getElementsByClassName('parent')[0],
    child = document.getElementsByClassName('parent')[0];

parent.style['padding-right'] = '100px';