Code:

<h2>搜索/过滤</h2>
<p>点击按钮显示下拉菜单，输入框可以搜索过滤内容。</p>

<div class="dropdown">
    <button onclick="myFunction()" class="dropbtn">下拉菜单</button>
    <div id="myDropdown" class="dropdown-content">
        <input type="text" placeholder="搜索.." id="myInput" onkeyup="filterFunction()">
        <a href="#about">About</a>
        <a href="#base">Base</a>
        <a href="#blog">Blog</a>
        <a href="#contact">Contact</a>
        <a href="#custom">Custom</a>
        <a href="#support">Support</a>
        <a href="#tools">Tools</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;
    }
    #myInput {
        border-box: box-sizing;
        background-image: url("data:image/png;base64,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");
        background-position: 14px 12px;
        background-repeat: no-repeat;
        font-size: 16px;
        padding: 14px 20px 12px 45px;
        border: none;
    }
    
    .dropdown {
        position: relative;
        display: inline-block;
    }
    
    .dropdown-content {
        display: none;
        position: absolute;
        background-color: #f6f6f6;
        min-width: 230px;
        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: #ddd}
    
    .show {display:block;}
</style>

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