DOM createElement

_divBG = document.createElement("div");
_divBG.style.position = "absolute";
_divBG.style.top  = 0;
_divBG.style.left = 0;
_divBG.style.backgroundColor = "black";
_divBG.style.width  = document.body.clientWidth;
_divBG.style.height = document.body.clientHeight;
_divBG.style.filter = "alpha(opacity=20)";
_divBG.style.zIndex = 99;
_divBG.style.display = "block";
	
document.body.appendChild(_divBG);