/* =============================================
   FONTS
   ============================================= */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap');

/* =============================================
   ROOT
   ============================================= */
:root {
    --bg:             #ffffff;
    --text:           #111827;
    --text-secondary: #374151;
    --text-muted:     #6b7280;
    --accent:         #2563eb;
    --accent-hover:   #1d4ed8;
    --border:         #d1d5db;
    --tag-bg:         #f3f4f6;

    --font:           'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-mono:      'JetBrains Mono', 'Fira Code', ui-monospace, monospace;
    --container:      680px;
}

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

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

body {
    font-family: var(--font);
    background-color: var(--bg);
    color: var(--text);
    line-height: 1.75;
    -webkit-font-smoothing: antialiased;
}

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

a:hover {
    text-decoration: underline;
    text-underline-offset: 2px;
}

ul { list-style: none; }
img { max-width: 100%; display: block; }

/* =============================================
   CONTAINER
   ============================================= */
.container {
    max-width: var(--container);
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* =============================================
   NAV
   ============================================= */
.site-nav {
    position: sticky;
    top: 0;
    background: rgba(255, 255, 255, 0.96);
    backdrop-filter: blur(6px);
    -webkit-backdrop-filter: blur(6px);
    border-bottom: 1px solid transparent;
    z-index: 100;
    transition: border-color 0.2s;
}

.site-nav.scrolled {
    border-bottom-color: var(--border);
}

.nav-inner {
    max-width: var(--container);
    margin: 0 auto;
    padding: 0 1.5rem;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.nav-name {
    font-family: var(--font-mono);
    font-size: 0.825rem;
    font-weight: 500;
    color: var(--text);
    text-decoration: none;
    letter-spacing: -0.01em;
}

.nav-name:hover {
    text-decoration: none;
    color: var(--text);
}

.nav-list {
    display: flex;
    gap: 1.75rem;
    list-style: none;
    align-items: center;
}

.nav-link {
    font-size: 0.825rem;
    color: var(--text-secondary);
    text-decoration: none;
    transition: color 0.15s;
}

.nav-link:hover,
.nav-link.active {
    color: var(--text);
    text-decoration: none;
}

/* Hamburger */
.hamburger {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 4px;
}

.hamburger span {
    display: block;
    width: 20px;
    height: 1.5px;
    background-color: var(--text);
}

@media (max-width: 540px) {
    .hamburger { display: flex; }

    .nav-list {
        display: none;
        position: fixed;
        top: 50px;
        left: 0;
        right: 0;
        flex-direction: column;
        gap: 0;
        background: var(--bg);
        border-bottom: 1px solid var(--border);
        padding: 0.75rem 0;
    }

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

    .nav-link {
        display: block;
        padding: 0.6rem 1.5rem;
        width: 100%;
    }
}

/* =============================================
   SITE HEADER (index only)
   ============================================= */
.site-header {
    padding: 5.5rem 0 3.5rem;
}

.site-header h1 {
    font-size: clamp(1.75rem, 4vw, 2.25rem);
    font-weight: 700;
    letter-spacing: -0.03em;
    line-height: 1.15;
    color: var(--text);
    margin-bottom: 0.4rem;
}

.header-subtitle {
    font-family: var(--font-mono);
    font-size: 0.825rem;
    font-weight: 400;
    color: var(--text-muted);
    margin-bottom: 1.5rem;
    letter-spacing: 0.01em;
}

.header-intro {
    font-size: 0.9625rem;
    color: var(--text-secondary);
    line-height: 1.85;
    margin-bottom: 1.75rem;
    max-width: 560px;
}

.header-links {
    display: flex;
    gap: 1.5rem;
    flex-wrap: wrap;
}

.header-link {
    font-size: 0.8rem;
    font-weight: 500;
    color: var(--text-secondary);
    text-decoration: none;
    background: var(--tag-bg);
    border: 1px solid var(--border);
    padding: 4px 11px;
    border-radius: 6px;
    transition: background 0.15s, border-color 0.15s, color 0.15s;
}

.header-link:hover {
    background: var(--border);
    border-color: #cbd5e1;
    color: var(--text);
    text-decoration: none;
}

/* =============================================
   SECTIONS
   ============================================= */
.section {
    padding: 3.25rem 0;
    border-top: 1px solid var(--border);
}

.section-label {
    font-family: var(--font-mono);
    font-size: 0.68rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    color: var(--text-muted);
    margin-bottom: 1.5rem;
}

.section-footer {
    margin-top: 1.5rem;
}

.section-footer a {
    font-size: 0.825rem;
}

/* =============================================
   ABOUT
   ============================================= */
.about-text {
    font-size: 1rem;
    color: var(--text);
    line-height: 1.85;
}

.about-text p + p {
    margin-top: 1.4rem;
}

/* =============================================
   SKILLS
   ============================================= */
.skills-block {
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}

.skill-row {
    display: flex;
    gap: 0.75rem;
    align-items: baseline;
    flex-wrap: wrap;
}

.skill-group-label {
    font-family: var(--font-mono);
    font-size: 0.72rem;
    font-weight: 500;
    color: var(--text-muted);
    min-width: 78px;
    flex-shrink: 0;
}

.skill-items {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.65;
}

/* =============================================
   PROJECTS — list entries
   ============================================= */
.project-list {
    display: flex;
    flex-direction: column;
}

.project-entry {
    padding: 1.5rem 0;
    border-bottom: 1px solid var(--border);
}

.project-entry:first-child {
    padding-top: 0;
}

.project-entry:last-child {
    border-bottom: none;
    padding-bottom: 0;
}

.project-entry-top {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 1rem;
    margin-bottom: 0.3rem;
}

.project-entry-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text);
    line-height: 1.35;
}

.project-entry-links {
    display: flex;
    gap: 0.35rem;
    flex-shrink: 0;
}

.entry-link {
    display: inline-flex;
    align-items: center;
    padding: 3px 9px;
    border-radius: 5px;
    border: 1px solid var(--border);
    background: transparent;
    font-family: var(--font-mono);
    font-size: 0.67rem;
    font-weight: 400;
    color: var(--text-muted);
    text-decoration: none;
    transition: all 0.15s ease;
}

.entry-link:hover {
    background: var(--text);
    color: var(--bg);
    border-color: var(--text);
    text-decoration: none;
}

.project-entry-desc {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: 0.65rem;
}

.entry-tags {
    display: flex;
    gap: 0.35rem;
    flex-wrap: wrap;
}

.tag {
    font-family: var(--font-mono);
    font-size: 0.67rem;
    color: var(--text-muted);
    background: var(--tag-bg);
    padding: 2px 7px;
    border-radius: 3px;
    font-weight: 400;
    letter-spacing: 0.02em;
}

/* =============================================
   RESEARCH — bibliography entries
   ============================================= */
.paper-list {
    display: flex;
    flex-direction: column;
}

.paper-entry {
    padding: 1.75rem 0;
    border-bottom: 1px solid var(--border);
}

.paper-entry:first-child {
    padding-top: 0;
}

.paper-entry:last-child {
    border-bottom: none;
    padding-bottom: 0;
}

.paper-entry-top {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: 1rem;
    margin-bottom: 0.2rem;
}

.paper-entry-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text);
    line-height: 1.4;
}

.paper-entry-year {
    font-family: var(--font-mono);
    font-size: 0.67rem;
    font-weight: 400;
    color: var(--text-muted);
    background: var(--tag-bg);
    border: 1px solid var(--border);
    padding: 2px 8px;
    border-radius: 4px;
    flex-shrink: 0;
    align-self: flex-start;
    font-variant-numeric: tabular-nums;
    letter-spacing: 0.02em;
}

.paper-entry-venue {
    font-size: 0.8rem;
    color: var(--text-muted);
    font-style: italic;
    margin-bottom: 0.2rem;
}

.paper-entry-authors {
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-bottom: 0.65rem;
}

.paper-entry-authors strong {
    color: var(--text-secondary);
    font-weight: 500;
}

.paper-entry-abstract {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    line-height: 1.82;
    margin-bottom: 0.75rem;
}

.paper-entry-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 0.75rem;
}

.paper-entry-links {
    display: flex;
    gap: 0.35rem;
}

/* =============================================
   CONTACT
   ============================================= */
.contact-intro {
    font-size: 1rem;
    color: var(--text);
    line-height: 1.8;
    margin-bottom: 1.25rem;
}

.contact-items {
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}

.contact-item {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 13px 16px;
    border: 1px solid var(--border);
    border-radius: 8px;
    text-decoration: none;
    background: transparent;
    transition: all 0.18s ease;
}

.contact-item:hover {
    border-color: var(--text-muted);
    background: var(--tag-bg);
    text-decoration: none;
    transform: translateX(3px);
}

.contact-key {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--text-muted);
    min-width: 64px;
    flex-shrink: 0;
    font-weight: 500;
    letter-spacing: 0.02em;
}

.contact-val {
    font-size: 0.875rem;
    color: var(--text-secondary);
    flex: 1;
}

.contact-arrow {
    font-size: 0.75rem;
    color: var(--text-muted);
    transition: color 0.18s, transform 0.18s;
}

.contact-item:hover .contact-arrow {
    color: var(--text);
    transform: translateX(2px);
}

/* =============================================
   FOOTER
   ============================================= */
.site-footer {
    padding: 2.5rem 0 3rem;
    border-top: 1px solid var(--border);
}

.site-footer p {
    font-size: 0.775rem;
    color: var(--text-muted);
}

/* =============================================
   BACK LINK (sub-pages)
   ============================================= */
.back-link {
    display: inline-flex;
    align-items: center;
    padding: 1.75rem 0 0;
    font-family: var(--font-mono);
    font-size: 0.72rem;
    font-weight: 500;
    color: var(--text-muted);
    text-decoration: none;
    letter-spacing: 0.03em;
    transition: color 0.15s;
}

.back-link:hover {
    color: var(--text);
    text-decoration: none;
}

/* =============================================
   PAGE HEADERS (sub-pages)
   ============================================= */
.page-header {
    padding: 4rem 0 2.75rem;
    border-bottom: 1px solid var(--border);
    margin-bottom: 0;
}

.page-header h1 {
    font-size: 1.625rem;
    font-weight: 700;
    letter-spacing: -0.025em;
    line-height: 1.2;
    margin-bottom: 0.35rem;
}

.page-header p {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

/* =============================================
   ABOUT PAGE — education timeline
   ============================================= */
.edu-list {
    display: flex;
    flex-direction: column;
    gap: 0;
}

.edu-entry {
    padding: 1rem 0;
    border-bottom: 1px solid var(--border);
    display: flex;
    gap: 1.5rem;
    align-items: flex-start;
}

.edu-entry:first-child { padding-top: 0; }
.edu-entry:last-child { border-bottom: none; padding-bottom: 0; }

.edu-years {
    font-size: 0.775rem;
    color: var(--text-muted);
    min-width: 90px;
    flex-shrink: 0;
    padding-top: 2px;
    font-variant-numeric: tabular-nums;
}

.edu-title {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text);
    margin-bottom: 0.1rem;
}

.edu-place {
    font-size: 0.825rem;
    color: var(--text-secondary);
}

/* =============================================
   PROJECTS PAGE — filter tabs
   ============================================= */
.filter-tabs {
    display: flex;
    gap: 0.4rem;
    flex-wrap: wrap;
    margin-bottom: 0;
    padding: 1.5rem 0;
}

.filter-btn {
    padding: 4px 13px;
    border-radius: 20px;
    border: 1px solid var(--border);
    background: transparent;
    color: var(--text-secondary);
    font-size: 0.775rem;
    font-family: var(--font);
    cursor: pointer;
    transition: all 0.15s;
}

.filter-btn:hover {
    border-color: var(--text-muted);
    color: var(--text);
}

.filter-btn.active {
    background: var(--text);
    border-color: var(--text);
    color: #fff;
}

/* =============================================
   RESPONSIVE
   ============================================= */
@media (max-width: 540px) {
    .project-entry-top {
        flex-direction: column;
        gap: 0.2rem;
    }

    .paper-entry-top {
        flex-direction: column;
        gap: 0.1rem;
    }

    .paper-entry-footer {
        flex-direction: column;
        align-items: flex-start;
    }

    .edu-entry {
        flex-direction: column;
        gap: 0.2rem;
    }
}

/* =============================================
   HERO
   ============================================= */
@keyframes fadeUp {
    from { opacity: 0; transform: translateY(22px); }
    to   { opacity: 1; transform: translateY(0); }
}

@keyframes scrollLine {
    0%, 100% { opacity: 0.3; }
    50%       { opacity: 0.85; }
}

.hero {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 5rem 1.5rem 6rem;
    text-align: center;
    position: relative;
}

.hero-avatar {
    width: 196px;
    height: 196px;
    border-radius: 50%;
    background: linear-gradient(145deg, #e5e7eb 0%, #d1d5db 100%);
    border: 3px solid #ffffff;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.08), 0 2px 8px rgba(0, 0, 0, 0.04);
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 1.75rem;
    font-family: var(--font-mono);
    font-size: 1.15rem;
    font-weight: 500;
    color: var(--text-muted);
    transition: transform 0.4s ease, box-shadow 0.4s ease;
    animation: fadeUp 0.6s ease both;
    overflow: hidden;
    cursor: default;
    user-select: none;
}

.hero-avatar img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    border-radius: 50%;
    display: block;
}

.hero-avatar:hover {
    transform: scale(1.04);
    box-shadow: 0 14px 44px rgba(0, 0, 0, 0.12);
}

.hero-name {
    font-size: clamp(2.25rem, 5vw, 3.25rem);
    font-weight: 700;
    letter-spacing: -0.04em;
    line-height: 1.1;
    color: var(--text);
    margin-bottom: 0.55rem;
    animation: fadeUp 0.6s ease 0.1s both;
}

.hero-tagline {
    font-family: var(--font-mono);
    font-size: 0.78rem;
    color: var(--text-muted);
    margin-bottom: 1.75rem;
    letter-spacing: 0.04em;
    animation: fadeUp 0.6s ease 0.2s both;
}

.hero-bio {
    font-size: 1.0625rem;
    color: var(--text);
    line-height: 1.78;
    max-width: 460px;
    margin: 0 auto 2.5rem;
    animation: fadeUp 0.6s ease 0.3s both;
}

.hero-buttons {
    display: flex;
    gap: 0.55rem;
    justify-content: center;
    flex-wrap: wrap;
    margin-bottom: 2.25rem;
    animation: fadeUp 0.6s ease 0.4s both;
}

.hero-btn {
    display: inline-flex;
    align-items: center;
    padding: 9px 20px;
    border-radius: 9999px;
    font-size: 0.845rem;
    font-weight: 500;
    font-family: var(--font);
    border: 1px solid var(--border);
    background: var(--bg);
    color: var(--text-secondary);
    text-decoration: none;
    transition: all 0.18s ease;
    cursor: pointer;
}

.hero-btn:hover {
    background: var(--text);
    color: var(--bg);
    border-color: var(--text);
    text-decoration: none;
    transform: translateY(-1px);
}

.hero-btn-primary {
    background: var(--text);
    color: var(--bg);
    border-color: var(--text);
}

.hero-btn-primary:hover {
    background: var(--text-secondary);
    border-color: var(--text-secondary);
    transform: translateY(-1px);
}

.hero-social {
    display: flex;
    gap: 0.5rem;
    justify-content: center;
    flex-wrap: wrap;
    animation: fadeUp 0.6s ease 0.5s both;
}

.hero-social-link {
    display: inline-flex;
    align-items: center;
    padding: 6px 14px;
    border-radius: 9999px;
    border: 1px solid var(--border);
    background: transparent;
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 400;
    color: var(--text-secondary);
    text-decoration: none;
    letter-spacing: 0.02em;
    transition: all 0.18s ease;
}

.hero-social-link:hover {
    background: var(--text);
    color: var(--bg);
    border-color: var(--text);
    text-decoration: none;
    transform: translateY(-1px);
}

.scroll-hint {
    position: absolute;
    bottom: 2rem;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
    animation: fadeUp 0.6s ease 0.85s both;
}

.scroll-hint span {
    font-family: var(--font-mono);
    font-size: 0.58rem;
    color: var(--text-muted);
    letter-spacing: 0.14em;
    text-transform: uppercase;
}

.scroll-hint::after {
    content: '';
    display: block;
    width: 1px;
    height: 28px;
    background: linear-gradient(to bottom, var(--text-muted), transparent);
    animation: scrollLine 2.2s ease-in-out infinite;
}

/* =============================================
   SECTION HEADINGS
   ============================================= */
.section-heading {
    font-size: clamp(1.4rem, 3vw, 1.875rem);
    font-weight: 700;
    letter-spacing: -0.03em;
    color: var(--text);
    line-height: 1.2;
    margin-bottom: 0.4rem;
}

.section-desc {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.65;
    margin-bottom: 2.25rem;
}

/* =============================================
   HERO RESPONSIVE
   ============================================= */
@media (max-width: 540px) {
    .hero {
        padding: 4rem 1.5rem 5rem;
    }

    .hero-avatar {
        width: 108px;
        height: 108px;
        font-size: 1rem;
    }

    .hero-buttons {
        flex-direction: column;
        align-items: stretch;
        width: 100%;
        max-width: 260px;
        margin-left: auto;
        margin-right: auto;
    }

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

    .hero-social {
        gap: 1rem;
        flex-wrap: wrap;
    }
}