act as expert web deplorer and make changes in below code as i say.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Stylish Project Portfolio</title>
    <link href="https://fonts.googleapis.com/css2?family=Montserrat:wght@400;600&display=swap" rel="stylesheet">
    <style>
        body {
            font-family: 'Montserrat', sans-serif;
            margin: 0;
            padding: 0;
            color: #333;
            background-color: #f3f2ef;
            font-size: 0.8em;
            display: flex;
        }
        header {
            background: #283e4a;
            color: white;
            display: flex;
            justify-content: flex-end;
            align-items: center;
            padding: 15px 48px;
            width: 100%;
            position: fixed;
            top: 10px;
            left: 0;
            box-sizing: border-box;
            box-shadow: 0 1.6px 4px rgba(0, 0, 0, 0.1);
        }
        nav {
            background: #fff;
            width: 128px;
            height: 100vh;
            padding-top: 144px;
            box-sizing: border-box;
            position: fixed;
            top: 0;
            left: 0;
            border-right: 0.8px solid #e0e0e0;
            box-shadow: 1.6px 0 4px rgba(0, 0, 0, 0.1);
            z-index: 2;
        }
        nav ul {
            list-style: none;
            padding: 0;
            margin: 0;
        }
        nav ul li {
            width: 100%;
        }
        nav ul li a {
            display: block;
            padding: 12px;
            color: #333;
            text-decoration: none;
            text-align: center;
            transition: background 0.3s, color 0.3s;
        }
        nav ul li a:hover, nav ul li a.active {
            background: #e6f3ff;
            color: #0073b1;
        }
        main {
            margin-left: 152px;
            padding: 96px 16px 16px;
            width: calc(100% - 176px);
            box-sizing: border-box;
        }
        section {
            padding: 16px;
            margin-bottom: 16px;
            background: #fff;
            border-radius: 6.4px;
            box-shadow: 0 3.2px 6.4px rgba(0, 0, 0, 0.1);
            display: none;
            opacity: 0;
            transform: translateY(16px);
            transition: all 0.4s ease-in-out;
        }
        section.visible {
            display: block;
            opacity: 1;
            transform: translateY(0);
        }
        section h2 {
            color: #0073b1;
            border-bottom: 1.6px solid #0073b1;
            padding-bottom: 4px;
            margin-bottom: 8px;
            font-weight: 600;
            font-size: 1.2em;
        }
        footer {
            text-align: center;
            padding: 8px 0;
            background: #283e4a;
            color: white;
            position: fixed;
            bottom: 10px;
            width: 100%;
            left: 0;
            box-shadow: 0 -1.6px 4px rgba(0, 0, 0, 0.1);
            font-size: 11.2px;
        } 
    </style>
</head>
<body>
    <header>
        <div>
            <h1>Project Portfolio</h1>
            <p>Showcasing My Work</p>
        </div>
    </header>

    <nav>
        <ul>
            <li><a href="#projects" onclick="showSection('projects')">Projects</a></li>
            <li><a href="#about" onclick="showSection('about')">About Me</a></li>
            <li><a href="#services" onclick="showSection('services')">Services</a></li>
            <li><a href="#contact" onclick="showSection('contact')">Contact</a></li>
        </ul>
    </nav>

    <main>
        <section id="projects">
            <h2>My Projects</h2>
            <div>
                <h3>Project Title</h3>
                <p>A brief description of the project showcasing its highlights and achievements.</p>
            </div>
        </section>

        <section id="about">
            <h2>About Me</h2>
            <p>Here is an introduction about myself and my journey in the field of work.</p>
        </section>

        <section id="services">
            <h2>Services</h2>
            <ul>
                <li>Service 1</li>
                <li>Service 2</li>
                <li>Service 3</li>
            </ul>
        </section>

        <section id="contact">
            <h2>Contact</h2>
            <p>I am available for freelance work. Reach out to me at <a href="mailto:contact@example.com">contact@example.com</a> or call (123) 456-7890.</p>
        </section>
    </main>

    <footer>
        <p>&copy; 2023 Stylish Project Portfolio</p>
    </footer>

    <script>
        function showSection(sectionId) {
            document.querySelectorAll('main section').forEach(section => {
                section.classList.remove('visible');
            });

            document.querySelectorAll('nav ul li a').forEach(link => {
                link.classList.remove('active');
            });

            document.getElementById(sectionId).classList.add('visible');
            document.querySelector(`nav ul li a[href="#${sectionId}"]`).classList.add('active');
        }

        window.onload = function() {
            showSection('projects');
        };
    </script>
</body>
</html>