body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}

header {
    background-color: #4CAF29;
    color: white;
    padding: 10px 20px;
}

nav a {
    color: white;
    margin-left: 20px;
    text-decoration: none;
}

.hidden {
    display: none;
}

.error {
    color: red;
}