css实现高度自适应

html, body {
    height: 100%;
    margin: 0px;
    padding: 0px;
}
#main {
    background-color: #999;
    height: 100%;
} 

#nav {
    background-color: #85d989;
    width: 100%;
    height: 50px;
}
#content {
    background-color: #cc85d9;
    width: 100%;
    position: absolute;
    top: 50px;
    bottom: 0px;
    left: 0px;
}