如何使用Bootstrap实现双层导航栏？求技术协助

你的现有代码仅包含搜索区域，缺少双层导航栏的核心结构，以下是符合需求的完整实现代码：

<!DOCTYPE html>
<html lang="es">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>双层导航栏示例</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.3.1/dist/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
</head>
<body>
    <!-- 上层导航栏：主导航 -->
    <nav class="navbar navbar-expand-lg navbar-light bg-white border-bottom">
        <div class="container">
            <a class="navbar-brand" href="#">你的品牌</a>
            <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#mainNav" aria-controls="mainNav" aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
            <div class="collapse navbar-collapse" id="mainNav">
                <ul class="navbar-nav ml-auto">
                    <li class="nav-item active">
                        <a class="nav-link" href="#">首页 <span class="sr-only">(当前)</span></a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">分类</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">关于我们</a>
                    </li>
                </ul>
            </div>
        </div>
    </nav>

    <!-- 下层导航栏：搜索区域 -->
    <nav class="navbar navbar-expand-lg navbar-light bg-light">
        <div class="container">
            <div class="d-flex w-100 justify-content-center">
                <div class="input-group mr-3" style="width: 40%;">
                    <input type="text" class="form-control" placeholder="¿Que Buscas?">
                </div>
                <div class="input-group mr-3" style="width: 25%;">
                    <input type="text" class="form-control" placeholder="Ciudad">
                </div>
                <button type="button" class="btn btn-danger">Buscar</button>
            </div>
        </div>
    </nav>

    <!-- Bootstrap JS依赖 -->
    <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
    <script src="https://cdn.jsdelivr.net/npm/popper.js@1.14.7/dist/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
    <script src="https://cdn.jsdelivr.net/npm/bootstrap@4.3.1/dist/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
</body>
</html>

关键调整说明： #

• 修正HTML结构：将样式表链接放到<head>标签内，符合标准规范
• 采用Bootstrap原生navbar组件构建双层导航，保证响应式适配
• 用container容器统一导航栏宽度，避免自定义padding-left导致的布局错位
• 搜索区域使用d-flex和input-group优化排版，提升视觉一致性
• 添加Bootstrap必需的JS依赖，确保导航栏的折叠功能正常工作

内容的提问来源于stack exchange，提问作者Joseph Nicholls Samper