问个 css 问题，为毛设置了 height，但是盒子的高度没变？

/* 首页iPhone */
.iphone.container {
    width:1000px;
    margin:0 auto;
    height:427px;
}
.iphone.warp{
    position:relative;
    padding:78px 20px;
    width:960px;
    height:427px;
    float:left;
}
.iphone.iphone-bg {
    position:absolute;
    top:78px;
    left:50%;
    margin-left:-106px;
    width:212px;
    height:427px;
    background: url(images/index_bg_iphone.png) no-repeat;
    float:left;
}

<div class="container hidden-l">
        <div class="iphone container">
            <div class="iphone warp">
                <div class="iphone iphone-bg fadein">

                </div>
            </div>
        </div>
    </div>