// use jQuery

function resizeContainer(){
		var naviHeight = $("#naviArea").height();
		var screenHeight = $("html").height();
		if (screenHeight > 700+50) {
			$("#naviArea").removeClass("positionRelative");
			$("#naviArea").addClass("positionFix");
		}else{
			$("#naviArea").removeClass("positionFix");
			$("#naviArea").addClass("positionRelative");
		}
	}
	
$(document).ready(function(){
	$(window).bind("resize", resizeContainer);
	$(window).bind("load", resizeContainer);
});