header{
    width:100%;
    height:45px;
    text-align: center;
    color: #fff;
    line-height: 45px;
    font-size: 18px;
    background-image: url('headerbg.png');
    position: fixed;
    left:0;
    top:0;
    z-index:9999;
  }
  nav{
    width:100%;
    height:50px;
    background: #fff;
    position: fixed;
    left:0;
    bottom:0;
    border-top:1px solid #ddd;
    z-index:9999;
  }
  nav ul{
    margin:0;
    width:100%;
    height:50px;
    padding:0;
  }
  nav ul li{
    width:20%;
    height:50px;
    float: left;
    text-align: center;
    padding-top:7px;
    list-style: none;
  }