/* --- UNIVERSAL STYLES --- */
body {
    font-family: Arial, sans-serif;
    margin: 0;
    background-color: #f4f4f9;
}

.app-container { /* Used for all main content containers */
    max-width: 800px;
    margin: 20px auto;
    background: #fff;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

header {
    background: #333;
    color: white;
    padding: 10px 0;
    text-align: center;
}
nav a {
    color: #fff;
    margin: 0 10px;
    text-decoration: none;
}
/* ... other universal styles like footer, h1, h2, link styles ... */