body {
    font-family: sans-serif;
    margin: 0;
    padding: 0;
}
header, footer {
    background: #f4f4f4;
    padding: 1rem;
    text-align: center;
}
nav ul {
    list-style: none;
    padding: 0;
    display: flex;
    justify-content: center;
    gap: 1rem;
}
nav a {
    text-decoration: none;
    color: #333;
}
nav a.active {
    font-weight: bold;
    border-bottom: 2px solid #333;
}
main {
    padding: 2rem;
}