dropdownlist覆盖div问题

只要在div前加上

<iframe position: absolute; z-index: 9; width: expression(this.nextSibling.offsetWidth);
    height: expression(this.nextSibling.offsetHeight); top: expression(this.nextSibling.offsetTop);
    left: expression(this.nextSibling.offsetLeft);" frameborder="0"></iframe>

就能解决此问题