<h2>可点击的下拉菜单</h2>
<p>点击按钮显示下拉菜单</p>
<div class="dropdown">
    <button onclick="myFunction()" class="dropbtn">下拉菜单</button>
    <div id="myDropdown" class="dropdown-content">
        <a href="#home">Home</a>
        <a href="#about">About</a>
        <a href="#contact">Contact</a>
    </div>
</div>
<style>
    .dropbtn {
        background-color: #4CAF50;
        color: white;
        padding: 16px;
        font-size: 16px;
        border: none;
        cursor: pointer;
    }
    
    .dropbtn:hover, .dropbtn:focus {
        background-color: #3e8e41;
    }
    
    .dropdown {
        position: relative;
        display: inline-block;
    }
    
    .dropdown-content {
        display: none;
        position: absolute;
        background-color: #f9f9f9;
        min-width: 160px;
        overflow: auto;
        box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
        z-index: 1;
    }
    
    .dropdown-content a {
        color: black;
        padding: 12px 16px;
        text-decoration: none;
        display: block;
    }
    
    .dropdown a:hover {background-color: #f1f1f1}
    
    .show {display:block;}
</style>
<script>
    /* 点击按钮，下拉菜单在 显示/隐藏 之间切换 */
    function myFunction() {
        document.getElementById("myDropdown").classList.toggle("show");
    }
    
    // 点击下拉菜单意外区域隐藏
    window.onclick = function(event) {
      if (!event.target.matches('.dropbtn')) {
    
        var dropdowns = document.getElementsByClassName("dropdown-content");
        var i;
        for (i = 0; i < dropdowns.length; i++) {
          var openDropdown = dropdowns[i];
          if (openDropdown.classList.contains('show')) {
            openDropdown.classList.remove('show');
          }
        }
      }
    }
</script>