Dojo dijit.form.button not loaded

http://stackoverflow.com/questions/10716530/dojo-dijit-form-button-not-loaded

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.7.2/dijit/themes/claro/claro.css">
<style type="text/css">
    body, html, #appLayout {
     height: 100%;
     width: 100%;
    }
</style>
<div id="appLayout">
</div>

JavaScript

require(["dijit/registry", "dijit/layout/BorderContainer", "dijit/layout/ContentPane", "dijit/form/Button", "dojo/query", "dojo/domReady!"], function(registry, BorderContainer,  ContentPane, Button, query){
        
var appLayout = new BorderContainer({
    design: "sidebar"
}, "appLayout");

var dataArea = new ContentPane({
    region: "center",
    content: '<div id="grid"></div>'
});

var actionArea = new ContentPane({
    region: "bottom",
    id: "actionarea"
});

var treeArea = new ContentPane({
    region: "left",
    id : "treearea",
    content: '<div id="treeroot"></div>',
    splitter: true
});

var button = new Button({
    label: "Load Computer tree",
    onClick:function(){
                            alert("carian sedang dilakukan");
                        }
}); 
actionArea.set('content', button);

appLayout.addChild(treeArea);
appLayout.addChild(dataArea);
appLayout.addChild(actionArea);
appLayout.startup();
button.startup();
     
});