Đã giải quyết Themes

    * {
  margin: 0;
  padding: 0;
}
#menu li {   LIST-STYLE-TYPE:none;}

#MENU {LIST-STYLE-TYPE:none;}
    

    @media screen and (min-width:801px) {
      #menu input {display:none;}
      
          #menu label {display:none;}

* {
  margin: 0;
  padding: 0;
}



.sub-menu  ul {
  background: #1F568B;
  list-style-type: none;
  text-align: center;
}
.sub-menu li {
  color: #f1f1f1;
  display: inline-block;
  width: 120px;
  height: 40px;
  line-height: 40px;
  margin-left: -5px;
}
.sub-menu a {
  text-decoration: none;
  color: #fff;
  display: block;
}
.sub-menu a:hover {
  background: #F1F1F1;
  color: #333;
}

}

          
            @media screen and (max-width: 800px) {
    

ul #menu{
  position:fixed;
  top:0;
  height:3em;
  margin:0;
  padding:0 10px;
  background:#333;
  color:#eee;
  box-shadow:0 -1px rgba(0,0,0,.5) inset;

}

ul #menu li{
  list-style-type:none;
  position:relative;
  width:100%;
}
label{
  position:relative;
  display:block;
  padding:0 18px 0 12px;
  line-height:3em;
  transition:background 0.3s;
  cursor:pointer;
}

label:after{
  content:"";
  position:absolute;
  display:block;
  top:50%;
  right:5px;
  width:0;
  height:0;
  border-top:4px solid rgba(255,255,255,.5);
  border-bottom:0 solid rgba(255,255,255,.5);
  border-left:4px solid transparent;
  border-right:4px solid transparent;
  transition:border-bottom .1s, border-top .1s .1s;
  }


input:checked ~ label:after{
  border-top:0 solid rgba(255,255,255,.5);
  border-bottom:4px solid rgba(255,255,255,.5);
}


input{display:none;}

input:checked ~ ul.sub-menu{
  max-height:300px;
  transition:max-height 0.5s ease-in;
}
input:checked ~ .sub-menu{height:240px;}

input:checked ~ label{background:rgba(0,0,0,.3);}

ul.sub-menu{
  max-height:0;
  padding:0;
  overflow:hidden;
  list-style-type:none;
  background:#444;
  box-shadow:0 0 1px rgba(0,0,0,.3);
  transition:max-height 0.5s ease-out;
  position:absolute;
  min-width:100%;
}


ul.sub-menu li a{
  display:block;
  padding:12px;
  color:#ddd;
  text-decoration:none;
  box-shadow:0 -1px rgba(0,0,0,.5) inset;
  transition:background .3s;
  white-space:nowrap;
}

ul.sub-menu li a:hover{
  background:rgba(0,0,0,.3);
}
}

<ul id="menu">
                        <li><input type="checkbox" id="checkbox-toggle"/><label for="checkbox-toggle">Menu</label>
                            <ul class="sub-menu">
                                <li><a href="#">Trang chủ</a></li>
                                <li><a href="#">Download</a></li>
                                <li><a href="#">Nạp thẻ</a></li>
                                <li><a href="#">Đăng ký</a></li>
                                <li><a href="#">Liên hệ</a></li>
                            </ul>
                        </li>
                    </ul>