/* Layout + navigation */
.header {
    position: sticky;
    top: 0;
    z-index: 50;
    background: rgba(14, 17, 22, .82);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--color-border);
}

.navbar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.brand {
    color: #fff;
    font-weight: 600;
    font-size: 1.05rem;
    letter-spacing: .5px;
    display: flex;
    align-items: center;
    gap: .55rem;
}

.brand img {
    width: 40px;
    height: 40px;
    object-fit: cover;
    border-radius: 50%;
    border: none;
}

.nav-toggle {
    background: none;
    border: 0;
    display: none;
    cursor: pointer;
    padding: .4rem;
    margin-right: -.4rem;
}

.nav-toggle span {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--color-text);
    position: relative;
    transition: var(--transition);
}

.nav-toggle span:before,
.nav-toggle span:after {
    content: '';
    position: absolute;
    left: 0;
    width: 100%;
    height: 2px;
    background: inherit;
    transition: inherit;
}

.nav-toggle span:before {
    top: -7px;
}

.nav-toggle span:after {
    top: 7px;
}

.nav-open .nav-toggle span {
    background: transparent;
}

.nav-open .nav-toggle span:before {
    transform: translateY(7px) rotate(45deg);
}

.nav-open .nav-toggle span:after {
    transform: translateY(-7px) rotate(-45deg);
}

/* Keep hamburger lines visible (user request: icon should not disappear when menu open) */
.nav-open .nav-toggle span,
.nav-open .nav-toggle span:before,
.nav-open .nav-toggle span:after {
    background: var(--color-text);
    transform: none;
}

.nav-menu {
    display: flex;
    gap: 1.2rem;
    list-style: none;
    margin: 0;
    padding: 0;
}

.nav-menu a {
    display: inline-block;
    padding: .55rem .2rem;
    font-size: .95rem;
    font-weight: 600;
    color: inherit;
    position: relative;
}

.nav-menu a:after {
    content: '';
    position: absolute;
    left: 0;
    bottom: 4px;
    height: 2px;
    width: 0;
    background: var(--color-accent);
    transition: var(--transition);
}

.nav-menu a:hover:after,
.nav-menu a.active:after {
    width: 100%;
}

/* Language dropdown */
.nav-lang details {
    position: relative;
}

.nav-lang summary {
    list-style: none;
    cursor: pointer;
    position: relative;
    padding: .55rem 1.5rem .55rem .2rem;
    font-size: .9rem;
    font-weight: 600;
}

.nav-lang summary .lang-label {
    transition: opacity .35s ease;
    display: inline-block;
}

.nav-lang summary::-webkit-details-marker {
    display: none;
}

.nav-lang details[open] summary {
    color: var(--color-secondary);
}

.lang-dropdown {
    list-style: none;
    margin: 0;
    padding: .4rem 0;
    position: absolute;
    top: 100%;
    left: 0;
    min-width: 120px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    box-shadow: var(--shadow-md);
    z-index: 200;
}

.lang-dropdown li {
    margin: 0;
}

.lang-dropdown a {
    display: block;
    padding: .45rem .9rem;
    font-size: .8rem;
    text-decoration: none;
}

.lang-dropdown a.active-lang {
    background: transparent;
    color: var(--color-secondary);
    font-weight: 600;
    /* emphasize current language */
    text-decoration: none;
}

/* Hover: show underline only (no background) */
.lang-dropdown a:hover {
    background: transparent;
    color: inherit;
    text-decoration: underline;
}

.lang-dropdown a[hreflang="zh-Hant"] {
    font-family: var(--font-zh);
}

.nav-lang summary:after {
    content: '\25BE';
    position: absolute;
    right: .22rem;
    top: 50%;
    transform: translateY(-55%);
    font-size: 1.05rem;
    line-height: 1;
    opacity: .9;
}

.nav-lang details[open] summary:after {
    transform: translateY(-55%) rotate(180deg);
}

@media (max-width: 860px) {
    .nav-lang details {
        width: 100%;
    }

    .lang-dropdown {
        position: static;
        border: 0;
        box-shadow: none;
        background: transparent;
        padding: .2rem 0 .4rem;
    }

    .lang-dropdown a {
        padding: .4rem 0;
    }

    .nav-toggle {
        display: block;
    }

    .nav-menu-wrapper {
        position: absolute;
        top: 64px;
        left: 0;
        width: 100%;
        background: var(--color-surface);
        border-bottom: 1px solid var(--color-border);
        box-shadow: var(--shadow-md);
        transform-origin: top center;
        transform: scaleY(0);
        transition: var(--transition);
    }

    .nav-open .nav-menu-wrapper {
        transform: scaleY(1);
    }

    .nav-menu {
        flex-direction: column;
        padding: .6rem 1.2rem 1.2rem;
    }

    .nav-menu a {
        display: block;
        /* full row clickable */
        width: 100%;
        padding: .75rem 0;
        /* consistent touch target */
    }

    /* Optional: highlight full row hover/active for better affordance */
    .nav-menu a:hover,
    .nav-menu a:focus {
        background: rgba(255, 255, 255, 0.03);
    }
}

.main-hero {
    display: grid;
    grid-template-columns: 340px 1fr;
    gap: 3rem;
    align-items: center;
}

.hero-photo {
    border-radius: var(--radius-md);
    overflow: hidden;
    box-shadow: none;
    position: relative;
    border: none !important;
}

.hero-photo img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    border: none;
    outline: none;
}

.hero-photo img:focus {
    outline: none;
    box-shadow: none;
}

.hero-photo:after {
    content: none;
}

.hero-text h1 span {
    color: var(--color-secondary);
}

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: .8rem;
    margin-top: 1rem;
}

/* Large screens: scale up hero layout */
@media (min-width: 1600px) {
    .main-hero {
        grid-template-columns: 400px 1fr;
        gap: 3.5rem;
    }
}

@media (min-width: 2000px) {
    .main-hero {
        grid-template-columns: 460px 1fr;
        gap: 4rem;
    }
}

@media (max-width: 960px) {
    .main-hero {
        grid-template-columns: 300px 1fr;
        gap: 2.2rem;
    }
}

@media (max-width: 760px) {
    .main-hero {
        grid-template-columns: 1fr;
    }

    .hero-photo {
        max-width: 340px;
    }
}

.timeline {
    position: relative;
    margin: 2rem 0;
    padding-left: 1.2rem;
}

.timeline:before {
    content: '';
    position: absolute;
    left: 6px;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--color-border);
}

.timeline-item {
    position: relative;
    margin-bottom: 1.8rem;
}

.timeline-item:last-child {
    margin-bottom: 0;
}

.timeline-point {
    position: absolute;
    left: -1px;
    top: 4px;
    width: 14px;
    height: 14px;
    background: var(--color-primary);
    border: 2px solid var(--color-bg);
    border-radius: 50%;
    box-shadow: 0 0 0 2px var(--color-primary);
}

.timeline-item h3 {
    margin: 0 0 .2rem;
    font-size: 1.05rem;
}

.timeline-item .meta {
    font-size: .75rem;
    letter-spacing: .5px;
    font-weight: 500;
    text-transform: uppercase;
    color: var(--color-secondary);
    margin-bottom: .4rem;
}

.pub-list {
    list-style: none;
    margin: 0;
    padding: 0;
}

.pub-item {
    padding: 1rem 0;
    border-bottom: 1px solid var(--color-border);
    display: grid;
    gap: .4rem;
}

.pub-item:last-child {
    border-bottom: 0;
}

.pub-item .title {
    font-weight: 600;
}

.pub-item .authors {
    font-size: .85rem;
    color: var(--color-muted);
}

.pub-item .journal {
    font-size: .75rem;
    letter-spacing: .5px;
    text-transform: uppercase;
    color: var(--color-secondary);
}

.pub-item a.pdf-link {
    font-size: .7rem;
    border: 1px solid var(--color-secondary);
    color: var(--color-secondary);
    padding: .2rem .55rem;
    border-radius: var(--radius-sm);
    text-decoration: none;
    margin-left: .5rem;
}

.pub-item a.pdf-link:hover {
    background: var(--color-secondary);
    color: #fff;
}

.honors-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    gap: clamp(1.2rem, 1.5vw, 2rem);
}

.honor-card {
    padding: 1rem 1rem 1.2rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    background: var(--color-surface);
    box-shadow: var(--shadow-sm);
    display: flex;
    flex-direction: column;
    gap: .4rem;
}

.honor-card h3 {
    font-size: 1rem;
    margin: 0;
}

.honor-card .year {
    font-size: .7rem;
    font-weight: 600;
    letter-spacing: .5px;
    color: var(--color-secondary);
}

/* Back to top floating button */
.back-to-top {
    position: fixed;
    right: 16px;
    bottom: 16px;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: var(--color-secondary);
    color: var(--color-text-invert);
    display: grid;
    place-items: center;
    border: 0;
    box-shadow: var(--shadow-md);
    cursor: pointer;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transform: translateY(8px);
    transition: opacity var(--transition), transform var(--transition), visibility var(--transition);
}

.back-to-top:hover,
.back-to-top:focus-visible {
    transform: translateY(0);
    box-shadow: 0 6px 24px rgba(0, 0, 0, 0.5);
    outline: none;
}

.back-to-top.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

@media (max-width: 640px) {
    .back-to-top {
        right: 12px;
        bottom: 12px;
        width: 42px;
        height: 42px;
    }
}