图片自动调整宽高



.p_list li a.p_img img{
    /**width:180px;  height:180px; 旧的样式*/
            max-height: 180px;
            max-width: 180px;
            width: expression( (this.width > 180 && this.width > this.height) ? '180px': this.width+'px');
            height: expression( (this.height > 180 && this.height > this.width) ? '180px': this.height+'px');
            border: 0px;
            vertical-align: middle;
        }