/* ==========================================
   Zheng Liu — Personal Website
   Modern Minimal Academic Portfolio
   ========================================== */

/* --- Reset & Base --- */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    --purple: #4B2E83;
    --purple-dark: #3a2368;
    --purple-light: #6b4fa3;
    --gold: #B7A57A;
    --gold-light: #d4c9a8;
    --text: #1a1a2e;
    --text-light: #555;
    --text-muted: #888;
    --bg: #ffffff;
    --bg-alt: #f8f7fc;
    --bg-dark: #1a1a2e;
    --border: #e8e5f0;
    --shadow: 0 2px 12px rgba(75, 46, 131, 0.08);
    --shadow-lg: 0 8px 30px rgba(75, 46, 131, 0.12);
    --radius: 10px;
    --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    color: var(--text);
    line-height: 1.7;
    background: var(--bg);
    -webkit-font-smoothing: antialiased;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 24px;
}

a {
    color: var(--purple);
    text-decoration: none;
    transition: color var(--transition);
}

a:hover {
    color: var(--purple-light);
}

img {
    max-width: 100%;
    height: auto;
}

/* --- Navigation --- */
#navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.85);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid transparent;
    transition: all var(--transition);
}

#navbar.scrolled {
    border-bottom-color: var(--border);
    box-shadow: 0 1px 8px rgba(0,0,0,0.06);
}

.nav-container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 24px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.nav-brand {
    font-family: 'Source Serif 4', Georgia, serif;
    font-weight: 700;
    font-size: 1.2rem;
    color: var(--purple) !important;
}

.nav-links {
    display: flex;
    list-style: none;
    gap: 8px;
}

.nav-links li a {
    padding: 6px 14px;
    border-radius: 6px;
    font-size: 0.88rem;
    font-weight: 500;
    color: var(--text-light);
    transition: all var(--transition);
}

.nav-links li a:hover,
.nav-links li a.active {
    color: var(--purple);
    background: rgba(75, 46, 131, 0.06);
}

.nav-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: 8px;
    flex-direction: column;
    gap: 5px;
}

.nav-toggle span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--text);
    border-radius: 2px;
    transition: var(--transition);
}

/* --- Hero Section --- */
#hero {
    padding: 140px 24px 80px;
    background: linear-gradient(135deg, var(--bg-dark) 0%, var(--purple-dark) 100%);
    color: white;
    min-height: 90vh;
    display: flex;
    align-items: center;
}

.hero-content {
    max-width: 1100px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    gap: 60px;
    width: 100%;
}

.hero-text {
    flex: 1;
}

.hero-label {
    font-size: 0.85rem;
    font-weight: 500;
    letter-spacing: 1.5px;
    text-transform: uppercase;
    color: var(--gold);
    margin-bottom: 12px;
}

#hero h1 {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: 3.5rem;
    font-weight: 700;
    line-height: 1.15;
    margin-bottom: 16px;
}

.hero-tagline {
    font-size: 1.15rem;
    line-height: 1.6;
    color: rgba(255, 255, 255, 0.8);
    margin-bottom: 32px;
}

.hero-stats {
    display: flex;
    gap: 32px;
    margin-bottom: 36px;
    flex-wrap: wrap;
}

.stat {
    display: flex;
    flex-direction: column;
}

.stat-number {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--gold);
}

.stat-label {
    font-size: 0.78rem;
    color: rgba(255, 255, 255, 0.6);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.hero-links {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
}

.btn {
    display: inline-block;
    padding: 10px 24px;
    border-radius: 8px;
    font-size: 0.9rem;
    font-weight: 600;
    transition: all var(--transition);
    cursor: pointer;
    border: none;
}

.btn-primary {
    background: var(--gold);
    color: var(--bg-dark);
}

.btn-primary:hover {
    background: var(--gold-light);
    color: var(--bg-dark);
    transform: translateY(-1px);
    box-shadow: 0 4px 16px rgba(183, 165, 122, 0.3);
}

.btn-outline {
    background: transparent;
    color: white;
    border: 1.5px solid rgba(255, 255, 255, 0.3);
}

.btn-outline:hover {
    border-color: white;
    color: white;
    background: rgba(255, 255, 255, 0.08);
}

.hero-image {
    flex-shrink: 0;
}

.hero-image img {
    width: 260px;
    height: 260px;
    border-radius: 50%;
    object-fit: cover;
    border: 4px solid rgba(255, 255, 255, 0.15);
    box-shadow: 0 16px 48px rgba(0, 0, 0, 0.3);
}

/* --- Sections --- */
.section {
    padding: 80px 0;
}

.section-alt {
    background: var(--bg-alt);
}

.section-title {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: 2rem;
    font-weight: 700;
    color: var(--purple);
    margin-bottom: 40px;
    position: relative;
    padding-bottom: 12px;
}

.section-title::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 48px;
    height: 3px;
    background: var(--gold);
    border-radius: 2px;
}

/* --- About --- */
.about-grid {
    display: grid;
    grid-template-columns: 1.4fr 1fr;
    gap: 48px;
    align-items: start;
}

.about-text p {
    margin-bottom: 16px;
    font-size: 1.02rem;
    color: var(--text);
}

.about-text p:last-child {
    margin-bottom: 0;
}

.detail-card {
    background: white;
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    margin-bottom: 16px;
    transition: all var(--transition);
    opacity: 0;
    transform: translateY(16px);
}

.detail-card.animate-in {
    opacity: 1;
    transform: translateY(0);
}

.detail-card h4 {
    font-size: 0.85rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--purple);
    margin-bottom: 12px;
}

.detail-card p {
    font-size: 0.92rem;
    margin-bottom: 4px;
    color: var(--text);
}

.detail-card ul {
    list-style: none;
    padding: 0;
}

.detail-card ul li {
    font-size: 0.92rem;
    padding: 3px 0;
    color: var(--text-light);
}

/* --- Research / Project Cards --- */
.research-grid {
    display: grid;
    gap: 20px;
}

.project-card {
    background: white;
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px;
    transition: all var(--transition);
    opacity: 0;
    transform: translateY(16px);
}

.project-card.animate-in {
    opacity: 1;
    transform: translateY(0);
}

.project-card:hover {
    box-shadow: var(--shadow-lg);
    border-color: rgba(75, 46, 131, 0.15);
}

.project-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
    flex-wrap: wrap;
    gap: 8px;
}

.project-meta {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}

.project-tag {
    display: inline-block;
    padding: 3px 10px;
    border-radius: 4px;
    font-size: 0.72rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.tag-active {
    background: #e8f5e9;
    color: #2e7d32;
}

.tag-published {
    background: #e3f2fd;
    color: #1565c0;
}

.tag-review {
    background: #fff3e0;
    color: #e65100;
}

.tag-role {
    background: #f3e5f5;
    color: var(--purple);
}

.tag-award {
    background: #fff8e1;
    color: #f57f17;
}

.project-date {
    font-size: 0.85rem;
    color: var(--text-muted);
    white-space: nowrap;
}

.project-card h3 {
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: 1.15rem;
    font-weight: 600;
    color: var(--text);
    margin-bottom: 8px;
    line-height: 1.4;
}

.project-lab {
    font-size: 0.88rem;
    color: var(--text-muted);
    margin-bottom: 4px;
}

.project-role {
    font-size: 0.88rem;
    color: var(--text-light);
    margin-bottom: 2px;
}

.project-advisors {
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 8px;
}

.project-details {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.5s ease;
}

.project-details.open {
    max-height: 2000px;
}

.project-details h4 {
    font-size: 0.88rem;
    font-weight: 600;
    color: var(--purple);
    margin: 16px 0 8px;
}

.project-details ul {
    padding-left: 20px;
    margin-bottom: 8px;
}

.project-details li {
    font-size: 0.9rem;
    line-height: 1.6;
    margin-bottom: 6px;
    color: var(--text-light);
}

.pub-list li {
    font-size: 0.85rem;
    color: var(--text-muted);
}

.expand-btn {
    margin-top: 12px;
    background: none;
    border: 1.5px solid var(--border);
    color: var(--purple);
    padding: 6px 16px;
    border-radius: 6px;
    font-size: 0.82rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition);
}

.expand-btn:hover {
    background: var(--purple);
    color: white;
    border-color: var(--purple);
}

/* --- Publications --- */
.pub-summary {
    display: flex;
    gap: 24px;
    margin-bottom: 40px;
    flex-wrap: wrap;
}

.pub-count {
    background: var(--bg-alt);
    padding: 16px 28px;
    border-radius: var(--radius);
    text-align: center;
    font-size: 0.88rem;
    color: var(--text-light);
    border: 1px solid var(--border);
}

.pub-count span {
    display: block;
    font-family: 'Source Serif 4', Georgia, serif;
    font-size: 2rem;
    font-weight: 700;
    color: var(--purple);
    margin-bottom: 2px;
}

.pub-group {
    margin-bottom: 32px;
}

.pub-group h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text);
    margin-bottom: 16px;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border);
}

.pub-entries {
    padding-left: 20px;
}

.pub-entries li {
    font-size: 0.92rem;
    line-height: 1.65;
    margin-bottom: 12px;
    color: var(--text-light);
}

.pub-entries li strong {
    color: var(--text);
}

.pub-entries li em {
    color: var(--purple);
}

/* --- Awards Timeline --- */
.awards-total {
    font-size: 1.05rem;
    color: var(--text-light);
    margin-bottom: 32px;
}

.timeline {
    position: relative;
    padding-left: 32px;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 7px;
    top: 8px;
    bottom: 8px;
    width: 2px;
    background: var(--border);
}

.timeline-item {
    position: relative;
    padding-bottom: 24px;
    opacity: 0;
    transform: translateX(-12px);
    transition: all 0.4s ease;
}

.timeline-item.animate-in {
    opacity: 1;
    transform: translateX(0);
}

.timeline-item::before {
    content: '';
    position: absolute;
    left: -29px;
    top: 6px;
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background: var(--gold);
    border: 2px solid white;
    box-shadow: 0 0 0 2px var(--gold);
}

.timeline-date {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--purple);
    margin-bottom: 4px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.timeline-content h4 {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text);
    margin-bottom: 2px;
}

.timeline-content p {
    font-size: 0.88rem;
    color: var(--text-muted);
}

/* --- Experience --- */
.experience-group {
    margin-bottom: 40px;
}

.experience-group h3 {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--purple);
    margin-bottom: 20px;
    padding-bottom: 8px;
    border-bottom: 2px solid var(--border);
}

.exp-item {
    padding: 20px 0;
    border-bottom: 1px solid var(--border);
    opacity: 0;
    transform: translateY(12px);
    transition: all 0.4s ease;
}

.exp-item.animate-in {
    opacity: 1;
    transform: translateY(0);
}

.exp-item:last-child {
    border-bottom: none;
}

.exp-header {
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    flex-wrap: wrap;
    gap: 8px;
}

.exp-header h4 {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text);
}

.exp-date {
    font-size: 0.82rem;
    color: var(--text-muted);
    white-space: nowrap;
}

.exp-org {
    font-size: 0.88rem;
    color: var(--text-muted);
    margin-bottom: 8px;
}

.exp-detail {
    font-size: 0.88rem;
    color: var(--text-light);
}

.exp-item ul {
    padding-left: 20px;
    margin-top: 4px;
}

.exp-item li {
    font-size: 0.9rem;
    line-height: 1.6;
    margin-bottom: 4px;
    color: var(--text-light);
}

/* Memberships */
.membership-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 12px;
}

.membership-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 16px;
    background: var(--bg-alt);
    border-radius: 8px;
    border: 1px solid var(--border);
}

.membership-item strong {
    font-size: 0.88rem;
    color: var(--text);
}

.membership-item span {
    font-size: 0.8rem;
    color: var(--text-muted);
    white-space: nowrap;
    margin-left: 12px;
}

/* --- Skills --- */
.skills-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 24px;
}

.skill-category {
    opacity: 0;
    transform: translateY(16px);
    transition: all 0.4s ease;
}

.skill-category.animate-in {
    opacity: 1;
    transform: translateY(0);
}

.skill-category h4 {
    font-size: 0.88rem;
    font-weight: 600;
    color: var(--text);
    margin-bottom: 12px;
}

.skill-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.skill-tag {
    display: inline-block;
    padding: 5px 14px;
    background: white;
    border: 1px solid var(--border);
    border-radius: 20px;
    font-size: 0.82rem;
    font-weight: 500;
    color: var(--text-light);
    transition: all var(--transition);
}

.skill-tag:hover {
    border-color: var(--purple);
    color: var(--purple);
    background: rgba(75, 46, 131, 0.04);
}

/* --- Gallery --- */
.gallery-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 20px;
}

.gallery-item {
    border-radius: var(--radius);
    overflow: hidden;
    cursor: pointer;
    transition: all var(--transition);
    background: white;
    border: 1px solid var(--border);
    opacity: 0;
    transform: translateY(16px);
}

.gallery-item.animate-in {
    opacity: 1;
    transform: translateY(0);
}

.gallery-item:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-4px);
}

.gallery-item.animate-in:hover {
    transform: translateY(-4px);
}

.gallery-item img {
    width: 100%;
    height: 220px;
    object-fit: cover;
    display: block;
    transition: transform 0.4s ease;
}

.gallery-item:hover img {
    transform: scale(1.03);
}

.gallery-caption {
    padding: 14px 16px;
}

.gallery-caption p {
    font-size: 0.85rem;
    line-height: 1.5;
    color: var(--text-light);
}

/* --- Lightbox --- */
.lightbox {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.92);
    z-index: 2000;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    padding: 40px;
    cursor: pointer;
}

.lightbox.active {
    display: flex;
}

.lightbox-close {
    position: absolute;
    top: 20px;
    right: 30px;
    color: white;
    font-size: 2rem;
    cursor: pointer;
    opacity: 0.7;
    transition: opacity var(--transition);
}

.lightbox-close:hover {
    opacity: 1;
}

#lightbox-img {
    max-width: 90%;
    max-height: 75vh;
    object-fit: contain;
    border-radius: 8px;
}

#lightbox-caption {
    color: rgba(255, 255, 255, 0.8);
    font-size: 0.9rem;
    text-align: center;
    margin-top: 16px;
    max-width: 600px;
    line-height: 1.5;
}

/* --- Footer --- */
footer {
    background: var(--bg-dark);
    color: rgba(255, 255, 255, 0.7);
    padding: 32px 0;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 16px;
}

.footer-content p {
    font-size: 0.88rem;
}

.footer-content a {
    color: var(--gold);
}

.footer-content a:hover {
    color: var(--gold-light);
}

.footer-links {
    display: flex;
    gap: 20px;
}

.footer-links a {
    font-size: 0.88rem;
    color: rgba(255, 255, 255, 0.6);
    transition: color var(--transition);
}

.footer-links a:hover {
    color: white;
}

/* --- Back to Top --- */
#backToTop {
    position: fixed;
    bottom: 32px;
    right: 32px;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: var(--purple);
    color: white;
    border: none;
    cursor: pointer;
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition);
    box-shadow: var(--shadow);
    z-index: 100;
}

#backToTop.visible {
    opacity: 1;
    visibility: visible;
}

#backToTop:hover {
    background: var(--purple-dark);
    transform: translateY(-2px);
}

/* --- Responsive --- */
@media (max-width: 900px) {
    .hero-content {
        flex-direction: column-reverse;
        text-align: center;
        gap: 32px;
    }

    .hero-stats {
        justify-content: center;
    }

    .hero-links {
        justify-content: center;
    }

    .hero-image img {
        width: 180px;
        height: 180px;
    }

    #hero h1 {
        font-size: 2.5rem;
    }

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

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

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

@media (max-width: 768px) {
    .nav-toggle {
        display: flex;
    }

    .nav-links {
        display: none;
        position: absolute;
        top: 64px;
        left: 0;
        right: 0;
        background: white;
        flex-direction: column;
        padding: 16px 24px;
        border-bottom: 1px solid var(--border);
        box-shadow: var(--shadow);
    }

    .nav-links.active {
        display: flex;
    }

    .section {
        padding: 56px 0;
    }

    #hero {
        padding: 120px 24px 56px;
        min-height: auto;
    }

    #hero h1 {
        font-size: 2rem;
    }

    .hero-stats {
        gap: 20px;
    }

    .stat-number {
        font-size: 1.4rem;
    }

    .section-title {
        font-size: 1.6rem;
    }

    .project-card {
        padding: 20px;
    }

    .exp-header {
        flex-direction: column;
        gap: 2px;
    }

    .membership-item {
        flex-direction: column;
        align-items: flex-start;
        gap: 4px;
    }

    .membership-item span {
        margin-left: 0;
    }

    .footer-content {
        flex-direction: column;
        text-align: center;
    }

    .pub-summary {
        flex-direction: row;
        gap: 12px;
    }

    .pub-count {
        flex: 1;
        padding: 12px 16px;
    }

    .pub-count span {
        font-size: 1.5rem;
    }
}

/* --- Animations --- */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.hero-text {
    animation: fadeInUp 0.8s ease forwards;
}

.hero-image {
    animation: fadeInUp 0.8s ease 0.2s forwards;
    opacity: 0;
}

/* Stagger animations for children */
.project-card:nth-child(2) { transition-delay: 0.05s; }
.project-card:nth-child(3) { transition-delay: 0.1s; }
.project-card:nth-child(4) { transition-delay: 0.15s; }
.project-card:nth-child(5) { transition-delay: 0.2s; }
.project-card:nth-child(6) { transition-delay: 0.25s; }
.project-card:nth-child(7) { transition-delay: 0.3s; }

.timeline-item:nth-child(2) { transition-delay: 0.05s; }
.timeline-item:nth-child(3) { transition-delay: 0.1s; }
.timeline-item:nth-child(4) { transition-delay: 0.15s; }
.timeline-item:nth-child(5) { transition-delay: 0.2s; }
.timeline-item:nth-child(6) { transition-delay: 0.25s; }
.timeline-item:nth-child(7) { transition-delay: 0.3s; }
.timeline-item:nth-child(8) { transition-delay: 0.35s; }
.timeline-item:nth-child(9) { transition-delay: 0.4s; }

.gallery-item:nth-child(2) { transition-delay: 0.1s; }
.gallery-item:nth-child(3) { transition-delay: 0.2s; }
.gallery-item:nth-child(4) { transition-delay: 0.3s; }
.gallery-item:nth-child(5) { transition-delay: 0.4s; }

.skill-category:nth-child(2) { transition-delay: 0.1s; }
.skill-category:nth-child(3) { transition-delay: 0.2s; }
.skill-category:nth-child(4) { transition-delay: 0.3s; }
.skill-category:nth-child(5) { transition-delay: 0.4s; }