/* Navigation — 固定導覽列：頂部透明，捲動後（.is-scrolled）變實底 */

.site-nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--nav-height);
    z-index: var(--z-nav);
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--spacing-md);
    padding: 0 var(--page-gutter);
    background: transparent;
    border-bottom: 1px solid transparent;
    transition: background var(--transition-normal), border-color var(--transition-normal), box-shadow var(--transition-normal);
}

.site-nav.is-scrolled,
.site-nav.is-open {
    background: var(--bg-overlay);
    backdrop-filter: blur(20px) saturate(1.4);
    -webkit-backdrop-filter: blur(20px) saturate(1.4);
    border-bottom-color: var(--border-color);
    box-shadow: 0 1px 32px rgba(0, 0, 0, 0.5);
}

/* ── 品牌 ── */
.brand-link {
    display: inline-flex;
    align-items: center;
    gap: 0.6rem;
    flex-shrink: 0;
}

.brand-logo {
    width: 36px;
    height: 36px;
}

.brand-text {
    font-family: var(--font-heading);
    font-size: 1.35rem;
    font-weight: 700;
    letter-spacing: 0.14em;
    color: var(--text-main);
    transition: color var(--transition-fast);
}

.brand-link:hover .brand-text { color: var(--primary-light); }

/* ── 連結 ── */
.nav-links {
    display: flex;
    align-items: center;
    gap: 0.25rem;
}

.nav-links a {
    position: relative;
    display: inline-flex;
    align-items: center;
    min-height: 44px;
    padding: 0.5rem 0.9rem;
    color: var(--text-muted);
    font-size: 0.95rem;
    font-weight: 500;
    letter-spacing: 0.03em;
    transition: color var(--transition-fast);
}

.nav-links a::after {
    content: '';
    position: absolute;
    left: 0.9rem;
    right: 0.9rem;
    bottom: 6px;
    height: 2px;
    background: var(--primary-color);
    transform: scaleX(0);
    transform-origin: left;
    transition: transform var(--transition-normal);
}

.nav-links a:hover,
.nav-links a[aria-current="page"] { color: var(--text-main); }

.nav-links a:hover::after,
.nav-links a[aria-current="page"]::after { transform: scaleX(1); }

.nav-links .nav-cta {
    margin-left: var(--spacing-xs);
    gap: 0.5rem;
    color: var(--text-main);
    background: var(--primary-tint);
    box-shadow: inset 0 0 0 1px var(--primary-border);
    clip-path: var(--clip-cut-sm);
}

.nav-links .nav-cta::after { display: none; }

.nav-links .nav-cta:hover {
    color: var(--bg-dark);
    background: var(--primary-color);
}

/* ── 漢堡按鈕 ── */
.hamburger {
    display: none;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 5px;
    width: 44px;
    height: 44px;
    border-radius: var(--radius-sm);
}

.hamburger span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--text-light);
    border-radius: 2px;
    transition: transform var(--transition-normal), opacity var(--transition-normal), background var(--transition-normal);
}

.hamburger.active span:nth-child(1) { transform: translateY(7px) rotate(45deg); background: var(--primary-color); }
.hamburger.active span:nth-child(2) { opacity: 0; }
.hamburger.active span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); background: var(--primary-color); }

/* ── 行動版：展開式選單 ── */
@media (max-width: 900px) {
    .site-nav { height: var(--nav-height-mobile); }

    .brand-logo { width: 30px; height: 30px; }

    .brand-text { font-size: 1.2rem; }

    .hamburger { display: flex; }

    .nav-links {
        position: fixed;
        top: var(--nav-height-mobile);
        left: 0;
        right: 0;
        flex-direction: column;
        align-items: stretch;
        gap: 0.25rem;
        padding: var(--spacing-sm) var(--page-gutter) var(--spacing-md);
        background: var(--bg-overlay-strong);
        border-bottom: 1px solid var(--border-color);
        box-shadow: 0 16px 32px rgba(0, 0, 0, 0.5);
        max-height: calc(100vh - var(--nav-height-mobile));
        overflow-y: auto;
        visibility: hidden;
        opacity: 0;
        transform: translateY(-8px);
        transition: opacity var(--transition-normal), transform var(--transition-normal), visibility var(--transition-normal);
    }

    .nav-links.active {
        visibility: visible;
        opacity: 1;
        transform: none;
    }

    .nav-links a {
        justify-content: center;
        padding: 0.9rem;
        font-size: 1.05rem;
        border-bottom: 1px solid var(--border-color);
    }

    .nav-links a::after { display: none; }

    .nav-links a[aria-current="page"] { color: var(--primary-light); }

    .nav-links .nav-cta {
        margin: var(--spacing-xs) 0 0;
        border-bottom: none;
    }
}