/* ---------- Responsive ---------- */
@media (max-width: 640px) {
    header nav {
        padding: var(--space-sm) var(--space-md);
        gap: var(--space-sm);
        flex-wrap: wrap;
    }

    .nav-toggle {
        display: flex;
    }

    .nav-links {
        display: none;
        width: 100%;
        flex-direction: column;
        gap: var(--space-xs);
        padding-top: var(--space-sm);
        border-top: 1px solid var(--color-border-light);
    }

    .nav-links a,
    .nav-logout-btn {
        font-size: 0.9rem;
        padding: var(--space-sm) var(--space-md);
        border-radius: var(--radius-md);
        width: 100%;
        text-align: left;
    }

    .nav-links a:hover,
    .nav-logout-btn:hover {
        background: var(--color-primary-glow);
    }

    .nav-links a.btn-primary {
        text-align: center;
        margin-top: var(--space-xs);
    }

    .nav-user {
        display: block;
        padding: var(--space-sm) var(--space-md);
        font-size: 0.85rem;
        color: var(--color-text-muted);
        border-bottom: 1px solid var(--color-border-light);
    }

    .nav-separator {
        display: none;
    }

    .auth-card {
        padding: var(--space-xl) var(--space-lg);
        border-radius: var(--radius-lg);
    }

    .hero {
        padding: var(--space-xl) var(--space-md);
    }

    .hero-actions {
        flex-direction: column;
    }

    .hero-actions .btn {
        width: 100%;
    }

    .hero-features {
        grid-template-columns: 1fr;
        padding: 0 var(--space-md);
    }

    .page-header,
    .page-content {
        padding: 0 var(--space-md);
    }

    .page-header-row {
        flex-direction: column;
        align-items: flex-start;
    }

    .book-grid {
        grid-template-columns: 1fr;
    }

    .stats-grid {
        grid-template-columns: 1fr;
    }

    .stat-card {
        padding: var(--space-md);
    }

    .stat-card-number {
        font-size: 1.6rem;
    }

    .form-card,
    .danger-card,
    .success-card,
    .verify-card {
        padding: var(--space-xl) var(--space-lg);
        border-radius: var(--radius-lg);
    }

    .mod-item-actions {
        flex-direction: column;
        align-items: flex-start;
    }

    .share-link {
        flex-direction: column;
    }

    .share-link input[type="text"] {
        width: 100%;
    }

    .danger-card .form-footer {
        flex-direction: column;
    }

    .error-page {
        padding: var(--space-2xl) var(--space-md);
    }

    .error-actions {
        flex-direction: column;
    }

    .error-actions .btn {
        width: 100%;
    }

    .torn-page {
        width: 140px;
        height: 170px;
    }

    .torn-page-number {
        font-size: 2.5rem;
    }

    .sealed-book-cover {
        width: 110px;
        height: 140px;
    }
}

/* ==========================================================================
   Error Pages
   ========================================================================== */

.error-page {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    min-height: calc(100vh - 200px);
    padding: var(--space-3xl) var(--space-lg);
    animation: fadeUp var(--duration-slow) var(--ease-out) both;
}

.error-illustration {
    margin-bottom: var(--space-xl);
}

.error-title {
    font-family: var(--font-display);
    font-size: clamp(2rem, 5vw, 3rem);
    font-weight: 600;
    line-height: 1.15;
    margin-bottom: var(--space-md);
    color: var(--color-text);
}

.error-subtitle {
    font-size: 1.05rem;
    line-height: 1.7;
    color: var(--color-text-secondary);
    max-width: 440px;
    margin: 0 auto var(--space-xl);
}

.error-actions {
    display: flex;
    gap: var(--space-md);
    justify-content: center;
    flex-wrap: wrap;
}

.error-trail {
    display: flex;
    gap: var(--space-sm);
    margin-top: var(--space-3xl);
}

.error-trail-dot {
    width: 5px;
    height: 5px;
    border-radius: 50%;
    background: var(--color-border);
    animation: trailPulse 2s ease-in-out infinite;
}

.error-trail-dot:nth-child(2) {
    animation-delay: 0.3s;
}

.error-trail-dot:nth-child(3) {
    animation-delay: 0.6s;
}

@keyframes trailPulse {
    0%, 100% { opacity: 0.3; transform: scale(1); }
    50% { opacity: 1; transform: scale(1.4); }
}