Hello everyone, guys

I've been having some trouble with styling an element in my page. Can any of u see the problem?

HTML Code:
<html>
	<head>
    	<script type="text/javascript">
			function Window() {
				this._getY = function() {
					return(window.innerHeight);
				}
				this._getX = function() {
					return(window.innerWidth);
				}
				this._load = function() {
					var w = document.getElementById("window");
						w.style.width = this._getX();
						w.style.height = this._getY();
				}
			}
			var WINDOW = new Window();
			WINDOW._load();
		</script>
        <style type="text/css">
			#window {
				display: block;
				position: absolute;
				top: 0px;
				left: 0px;
				background-color:red;
			}
		</style>
    </head>
    <body>
    	<div id="window">
        	Content 
        </div>
    </body>
</html>
I have tryed to alert the methods _getX() and _getY(), and both functions are working pretty. I think the problem it's on the styling thing, or getting the element on the page.

Maybe there's a simple error that I'm not seeing, i've spent too much time using Jquery, so probably I got too confortable on that.

Sorry for my bad english, it's not my native language.
Thank you all