Buttons can be created as follows:
var button = Ext.create('Ext.Button', {
iconCls: 'refresh',
iconMask: true
});
Ext.Viewport.add( { xtype: 'container', padding: 10, items: [button] });
normal - a basic gray button
back - a back button
forward - a forward button
round - a round button
action - shaded using the $base-color (dark blue by default)
decline - red
confirm - green