[ExtJS] Form Scrolling

HTML

<link rel="stylesheet" href="http://dev.sencha.com/deploy/ext-4.0.2a/resources/css/ext-all-gray.css">

JavaScript

var formPanel = Ext.create('Ext.form.Panel', {
    title: 'Tab 1',
    height: 250,
    width: 400,
    bodyPadding: 10,
    items: [  {
        fieldLabel: 'Striping',
        xtype:'radiogroup',
        columns: [50, 100],
        items: [{
            boxLabel: 'Yes',
            name: 'rb',
            id: 'stYes',
          /*  checked: true,*/
            inputValue: '1'

        }, 
        {
            boxLabel: 'No',
            name: 'rb',
            id: 'stNo',
            inputValue: '2'
        }],
        listeners: {
            change: function( radiogroup, newValue, oldValue, eOpts ) {
                alert(newValue.rb);
            }
        }
    }]
});

var tabPanel = Ext.create('Ext.tab.Panel', {
    height: 150,
    items: [formPanel]
});

Ext.create('Ext.container.Viewport', {
    layout: 'fit',
    renderTo: Ext.getBody(),
    items: [tabPanel]
});