JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://dev.sencha.com/deploy/ext-3.4.0/resources/css/ext-all.css">
<script src="http://dev.sencha.com/deploy/ext-3.4.0/adapter/ext/ext-base.js"></script>
<script src="http://dev.sencha.com/deploy/ext-3.4.0/ext-all.js"></script>

CSS

body{
    background:#ffa;
    margin:10px;
}

JavaScript

var form = new Ext.form.FormPanel({
    border: false,
    renderTo: Ext.getBody(),
    bodyStyle:'background:#DFE8F6', //or if you set it to none, you will see through it.
    layout: 'fit',
    items: [{
        xtype: 'tabpanel',
        activeTab: 0,
        bodyStyle: 'background:none',
        deferredRender: false,
        defaults: {
            bodyStyle: 'padding: 4px;background:none',
            layout: 'form',
            autoScroll: true
        },
        items: [{
            title: 'Tab 1',
            html: 'Tab 1'
        }, {
            title: 'Tab 2',
            html: 'Tab 2'
        }, {
            title: 'Tab 3',
            html: 'Tab 3'
        }]
    }]]
    }]
});