JSFiddle - React, Tailwind, and code Playground

CSS

.myclass{width: 120px;height: 50px;border: 1px solid red;}
.ff-class{background: #eee}
.ie-class{background: #fce}

JavaScript

this.body = new Element('div', {'class': 'myclass'}).inject(document.body);
if (Browser.Engine.trident4) this.body.addClass('ie-class');
        /////
if (Browser.Engine.gecko) this.body.addClass('ff-class');