点击按钮切换css样式

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>切换CSS样式示例</title>
    <style>
        .btn {
            padding: 10px 20px;
            font-size: 16px;
            cursor: pointer;
        }
        .btn-primary {
            background-color: blue;
            color: white;
        }
        .btn-secondary {
            background-color: gray;
            color: black;
        }
    </style>
</head>
<body>
    <button id="toggleBtn" class="btn btn-primary">切换样式</button>

    <script>
        document.getElementById('toggleBtn').addEventListener('click', function() {
            const btn = document.getElementById('toggleBtn');
            if (btn.classList.contains('btn-primary')) {
                btn.classList.remove('btn-primary');
                btn.classList.add('btn-secondary');
            } else {
                btn.classList.remove('btn-secondary');
                btn.classList.add('btn-primary');
            }
        });
    </script>
</body>
</html>