jquery 页面向下滚动

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>jQuery Scroll Example</title>
    <style>
        body {
            height: 2000px; /* 设置一个较大的高度以便测试滚动 */
        }
        .navbar {
            position: fixed;
            top: 0;
            width: 100%;
            background-color: transparent;
            transition: background-color 0.3s;
        }
    </style>
</head>
<body>
    <div class="navbar">Navigation Bar</div>

    <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
    <script>
        $(document).ready(function() {
            $(window).scroll(function() {
                var scrollTop = $(this).scrollTop();
                if (scrollTop > 100) { // 当滚动超过100px时
                    $('.navbar').css('background-color', 'rgba(0, 0, 0, 0.8)');
                } else {
                    $('.navbar').css('background-color', 'transparent');
                }
            });
        });
    </script>
</body>
</html>