解决IE6不支持position:fixed的Bug

/* 除IE6浏览器的通用方法 */

.ie6fixedTL{position:fixed;left:0;top:0}
.ie6fixedBR{position:fixed;right:0;bottom:0}

/* IE6浏览器的特有方法 */

/* 修正IE6振动bug */

* html,* html body{background-image:url(about:blank);background-attachment:fixed}
* html .ie6fixedTL{position:absolute;left:expression(eval(document.documentElement.scrollLeft));top:expression(eval(document.documentElement.scrollTop))}
* html .ie6fixedBR{position:absolute;left:expression(eval(document.documentElement.scrollLeft+document.documentElement.clientWidth-this.offsetWidth)-(parseInt(this.currentStyle.marginLeft,10)||0)-(parseInt(this.currentStyle.marginRight,10)||0));top:expression(eval(document.documentElement.scrollTop+document.documentElement.clientHeight-this.offsetHeight-(parseInt(this.currentStyle.marginTop,10)||0)-(parseInt(this.currentStyle.marginBottom,10)||0)))}