html/css背景图片自适应分辨率大小

<style type='text/css'>
    .bgbox {
        position: absolute;
        left: 0;
        top: 0;
        width: 100%;
        overflow: hidden;
        bottom: 0px;
    }
    .bgbox-items {
        overflow: visible;
    }
    .bgbox-items,
    .bgbox-items-item{
        position: absolute;
        left: 0;
        top: 0;
        width: 100%;
        height: 100%;
        overflow: hidden;
    }
    .bgbox-items-item {
        background: #fff none no-repeat center center;
        -webkit-background-size: cover;
        -moz-background-size: cover;
        -o-background-size: cover;
        background-size: cover;
    }
</style>
<!--[if lte IE 8]>
<style>
.bgbox-items-item1 {
    filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src="data:images/mainbg.png", sizingMethod="scale");
}
</style><![endif]-->

　　

<div class='bgbox'>
    <div class='bgbox-items'>
        <div class='bgbox-items-item bgbox-items-item1' style='background-image:url(images/mainbg.png)'></div>
    </div>
</div>