*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f0f4f8;
    color: #2d3748;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ── Header ─────────────────────────────────────────────── */
header {
    background-color: #1a365d;
    color: #ffffff;
    padding: 1.25rem 2rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.3);
}

header h1 {
    font-size: 1.4rem;
    letter-spacing: 0.05em;
    color: #90cdf4;
}

/* ── Navigation ──────────────────────────────────────────── */
nav {
    display: flex;
    gap: 0.5rem;
}

nav a {
    color: #bee3f8;
    text-decoration: none;
    padding: 0.4rem 0.9rem;
    border-radius: 4px;
    font-size: 0.9rem;
    transition: background-color 0.2s, color 0.2s;
}

nav a:hover {
    background-color: #2b6cb0;
    color: #ffffff;
}

nav a.active {
    background-color: #2c5282;
    color: #ffffff;
    font-weight: 600;
}

/* ── Main content ────────────────────────────────────────── */
main {
    flex: 1;
    max-width: 860px;
    width: 100%;
    margin: 3rem auto;
    padding: 0 1.5rem;
}

.card {
    background-color: #ffffff;
    border-radius: 8px;
    padding: 2.5rem 3rem;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1), 0 4px 12px rgba(0, 0, 0, 0.06);
}

.card h2 {
    font-size: 2rem;
    color: #1a365d;
    margin-bottom: 1rem;
    border-bottom: 3px solid #4299e1;
    padding-bottom: 0.5rem;
    display: inline-block;
}

.card p {
    margin-top: 1rem;
    line-height: 1.7;
    color: #4a5568;
    font-size: 1rem;
}

/* ── Footer ──────────────────────────────────────────────── */
footer {
    background-color: #1a365d;
    color: #718096;
    text-align: center;
    padding: 1rem;
    font-size: 0.8rem;
}

/* ── Hamburger button (hidden on desktop) ────────────────── */
.nav-toggle {
    display: none;
}

/* ── Responsive ──────────────────────────────────────────── */
@media (max-width: 640px) {
    header {
        flex-wrap: wrap;
        padding: 1rem;
    }

    header h1 {
        font-size: 1.2rem;
    }

    .nav-toggle {
        display: flex;
        flex-direction: column;
        justify-content: space-between;
        width: 28px;
        height: 20px;
        background: none;
        border: none;
        cursor: pointer;
        padding: 0;
    }

    .nav-toggle span {
        display: block;
        height: 2px;
        background-color: #bee3f8;
        border-radius: 2px;
        transition: transform 0.2s, opacity 0.2s;
    }

    header.nav-open .nav-toggle span:nth-child(1) {
        transform: translateY(9px) rotate(45deg);
    }

    header.nav-open .nav-toggle span:nth-child(2) {
        opacity: 0;
    }

    header.nav-open .nav-toggle span:nth-child(3) {
        transform: translateY(-9px) rotate(-45deg);
    }

    nav {
        display: none;
        flex-direction: column;
        width: 100%;
        gap: 0.25rem;
        padding-top: 0.5rem;
    }

    header.nav-open nav {
        display: flex;
    }

    nav a {
        padding: 0.6rem 1rem;
        text-align: center;
    }

    main {
        margin: 1.5rem auto;
        padding: 0 1rem;
    }

    .card {
        padding: 1.5rem;
    }

    .card h2 {
        font-size: 1.5rem;
    }
}