index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="style.css">
</head>
<body>
    <header>
        <div class="container">
            <nav class="navbar">
                <a href="#" class="nav-branding">DEV</a>
                <ul class="nav-menu">
                    <li class="nav-item"><a href="#" class="nav-link">Home</a></li>
                    <li class="nav-item"><a href="#" class="nav-link">About</a></li>
                    <li class="nav-item"><a href="#" class="nav-link">Contact</a></li>
                </ul>
                <div class="hamburger">
                    <span class="bar"></span>
                    <span class="bar"></span>
                    <span class="bar"></span>
                </div>
            </nav>
        </div>
    </header>
</body>
<script>
    let hamburger = document.querySelector(".hamburger");
    let navmenu   = document.querySelector(".nav-menu");

    hamburger.addEventListener("click", () => {
        hamburger.classList.toggle("active");
        navmenu.classList.toggle("active");
    });

    document.querySelectorAll(".nav-link").forEach(n =>
        n.addEventListener("click", () => {
            hamburger.classList.remove("active");
            navmenu.classList.remove("active")
        })
    )
</script>
</html>