JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://dev.sencha.com/deploy/ext-3.3.1/resources/css/ext-all.css">
<script src="http://dev.sencha.com/deploy/ext-3.3.1/adapter/ext/ext-base.js"></script>
<script src="http://dev.sencha.com/deploy/ext-3.3.1/ext-all-debug.js"></script>

CSS

body {
    overflow: hidden;
}

JavaScript

Ext.onReady(function() {
    var win = new Ext.Window({
        draggable: false
    });

    win.show();

    win.setSize(Ext.getBody().getViewSize().x/2,Ext.getBody().getViewSize().y/2);
    win.setPagePosition(0, 0);
    Ext.fly(window).on('resize', function(e, w) {
        win.setSize(Ext.getBody().getViewSize());
        win.setPagePosition(0, 0);
    });
});