<div class="wrap">
    <ul class="nav">
      <li><a href="#">首頁</a> </li>
      <li><a href="#">聯絡我們</a></li>
      <li class="button">
        <a href="#">產品查詢</a>
        <ul class="nav-hide">
          <li>1</li>
          <li>2</li>
          <li>3</li>
          <li>4</li>
        </ul>
      </li>
    </ul>
  </div>
.wrap{
  max-width:900px;
  margin:0 auto;
  background-color: yellow;
}
.nav{
  display:flex;
  justify-content: flex-end;
}
.nav li{
  width:25%;
  border:1px solid black;
  text-align:center;
  font-size:20px;
  font-weight: 600;
}
.nav li a{
  display:block;
  padding-top:10px;
  padding-bottom:10px;
  text-decoration: none;
}
.nav li a:hover{
  background-color:red;
  color:white;
}
.nav-hide li{
  width:100%;
  padding:0;
  padding-top:10px;
  padding-bottom:10px;
}
.button{
  position:relative;
}
.nav-hide{
  position:absolute;
  display:none;
  top:40px;
  left:0;
  right:0;
}
$(document).ready(function(){
 
  $('.button').click(function(e){
    e.preventDefault();
    $('.nav-hide').slideToggle();
  })
})

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js