#header{display:none;} /*将默认的导航头屏蔽掉，这样才能把自己的导航栏加上去*/
*{
margin:0;
padding:0;
box-sizing: border-box;
font-family: sans-serif;
}
body{
     background-color: #efefef;
 background-image:url(https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1543510441070&di=135081c289fd5f0f1fa3d55844f30d8f&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201502%2F09%2F20150209140201_hULNE.jpeg);
     background-repeat: no-repeat; 
     background-attachment: fixed; 
     background-position: center  53%; 
     background-size: cover; 
    padding-top:0px;

}

#shwtop ul{
     margin:0;
     paddin:0;
     list-style-type:none;
     overflow:hidden;
}

#shwtop li{
   float:left;
}

#shwtop li a, .dropbtn{
     display:inline-block;
  color:#6699CC;
 
     text-alingn:center;
     padding:14px 16px;
     font-size:20px;
     text-decoration:none;
}

/*鼠标移到导航条时，背景颜色修改*/
#shwtop li a:hover, .dropdown:hover .dropbtn{
 background-color:#CCCCFF;
  <!-- background-color:#FFCC99;-->
    opacity:0.5;
}