透明PNG格式图片兼容IE6浏览器
background:url("xxxx.png") no-repeat ;_background-image:none;
_filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='xxxx.png',sizingMethod='scale');
_filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='xxxx.png',sizingMethod='scale');