JSFiddle - React, Tailwind, and code Playground

HTML

<div id="box">Hi</div>

CSS

#box {
    width: 300px;
    height: 100px;
    border: 2px solid red;
    background: #DDD;
    margin: 100px;
    padding: 20px;
    border-radius: 5px;
}

JavaScript

Element.Styles.combine({
    borderRadius: '@px'
});

var fx = new Fx.Tween('box',{
    property: 'border-radius',
    duration: 'long'
});
fx.start(5,100);