var el = "banner_image";
var bgimg = new Array("../images/banner1.jpg", "../images/banner2.jpg", "../images/banner3.jpg", "../images/banner4.jpg", "../images/banner5.jpg", "../images/banner6.jpg", "../images/banner7.jpg");
var random = Math.round((bgimg.length - 1) * Math.random());
var cssStr = "#" + el + " { background:url(" + bgimg[random] + ") no-repeat top left; background-size:100% auto; }";
var style = document.createElement("style");
style.setAttribute("type", "text/css");
if(style.styleSheet) {
	style.styleSheet.cssText = cssStr;
} else {
	var cssText = document.createTextNode(cssStr);
	style.appendChild(cssText);
}
document.getElementsByTagName("head")[0].appendChild(style);