var cssAray = ["common/css/top_bg001.css","common/css/top_bg002.css","common/css/top_bg003.css","common/css/top_bg004.css","common/css/top_bg005.css","common/css/top_bg006.css"];
var css = cssAray[Math.floor(Math.random() * cssAray.length)];
document.getElementById("bgrandom").href = css;