HTML Simple Flexbox Layout

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Flexbox Layout</title>
    <style>
        * {
            box-sizing: border-box;
        }

        body {
            margin: 0;
            font-family: Arial, sans-serif;
            color: #333;
        }

        .page {
            display: flex;
            flex-direction: column;
            min-height: 100vh;
        }

        .site-header {
            background: #4caf50;
            padding: 20px;
            text-align: center;
            font-weight: bold;
        }

        .main-nav {
            background: #ffeb3b;
            padding: 15px;
            text-align: center;
            font-weight: bold;
        }

        .content-wrap {
            display: flex;
            flex: 1;
        }

        .sidebar {
            background: #ff9800;
            width: 25%;
            padding: 20px;
            font-weight: bold;
        }

        .content {
            background: #90caf9;
            flex: 1;
            padding: 20px;
            font-weight: bold;
        }

        .site-footer {
            background: #e57373;
            padding: 20px;
            text-align: center;
            font-weight: bold;
        }

        @media (max-width: 600px) {
            .content-wrap {
                flex-direction: column;
            }

            .sidebar {
                width: 100%;
            }
        }
    </style>
</head>
<body>
    <div class="page">
        <header class="site-header">
            <h1>Header</h1>
        </header>

        <nav class="main-nav" aria-label="Main navigation">
            Navigation
        </nav>

        <div class="content-wrap">
            <aside class="sidebar">
                <h2>Aside</h2>
            </aside>

            <main class="content">
                <h2>Main Content</h2>
            </main>
        </div>

        <footer class="site-footer">
            Footer
        </footer>
    </div>
</body>
</html>