The question is how you want your content to be displayed? If you want to hide the offscreen elements, you can do that by editting the html output. By default it will use 100% as values for the width and height. Here is a simple sample with an offscreen yellow ball.
Note the ball is shown, when it should not be and the entire page is white. The background color of the html is set to #ccc.
Now by editing the width and height values in the html file to match the stage's defined values, I get this:
As you can see, no yellow ball and the html is showing it's bg color. There are 3 references to the width and height in the file so make sure you adjust all 3.
Hope this helps,
Chris