/* ===================================
   CSS Variables & Design System
   =================================== */
:root {
    /* Color Palette */
    --primary-color: #2c5f8d;
    --primary-dark: #1e4464;
    --primary-light: #4a90d9;
    --secondary-color: #4a90d9;
    --accent-color: #e67e22;
    --accent-hover: #d35400;

    /* Text Colors */
    --text-primary: #2c3e50;
    --text-secondary: #7f8c8d;
    --text-light: #95a5a6;
    --text-white: #ffffff;

    /* Background Colors */
    --bg-primary: #ffffff;
    --bg-secondary: #f8f9fa;
    --bg-tertiary: #ecf0f1;
    --bg-dark: #34495e;

    /* Border Colors */
    --border-color: #e1e8ed;
    --border-light: #ecf0f1;

    /* Shadow Colors */
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 40px rgba(0, 0, 0, 0.15);

    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-secondary: Georgia, 'Times New Roman', serif;

    /* Font Sizes */
    --fs-xs: 0.75rem;      /* 12px */
    --fs-sm: 0.875rem;     /* 14px */
    --fs-base: 1rem;       /* 16px */
    --fs-lg: 1.125rem;     /* 18px */
    --fs-xl: 1.25rem;      /* 20px */
    --fs-2xl: 1.5rem;      /* 24px */
    --fs-3xl: 1.875rem;    /* 30px */
    --fs-4xl: 2.25rem;     /* 36px */
    --fs-5xl: 3rem;        /* 48px */

    /* Line Heights */
    --lh-tight: 1.2;
    --lh-normal: 1.6;
    --lh-loose: 1.8;

    /* Spacing */
    --spacing-xs: 0.5rem;   /* 8px */
    --spacing-sm: 1rem;     /* 16px */
    --spacing-md: 2rem;     /* 32px */
    --spacing-lg: 4rem;     /* 64px */
    --spacing-xl: 6rem;     /* 96px */

    /* Layout */
    --max-width: 1200px;
    --header-height: 70px;

    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    --radius-full: 9999px;

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 300ms ease;
    --transition-slow: 500ms ease;
}

/* ===================================
   Reset & Base Styles
   =================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

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

body {
    font-family: var(--font-primary);
    font-size: var(--fs-base);
    line-height: var(--lh-normal);
    color: var(--text-primary);
    background-color: var(--bg-primary);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* ===================================
   Typography
   =================================== */
h1, h2, h3, h4, h5, h6 {
    font-weight: 600;
    line-height: var(--lh-tight);
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
}

h1 {
    font-size: clamp(2rem, 5vw, 3.5rem);
}

h2 {
    font-size: clamp(1.75rem, 4vw, 2.5rem);
}

h3 {
    font-size: clamp(1.25rem, 3vw, 1.75rem);
}

h4 {
    font-size: var(--fs-xl);
}

p {
    margin-bottom: var(--spacing-sm);
    line-height: var(--lh-loose);
}

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

a:hover {
    color: var(--primary-dark);
}

em {
    font-style: italic;
    font-family: var(--font-secondary);
}

/* ===================================
   Utility Classes
   =================================== */
.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 var(--spacing-sm);
}

.section {
    padding: var(--spacing-lg) 0;
}

.section-title {
    text-align: center;
    margin-bottom: var(--spacing-md);
    position: relative;
}

.section-title::after {
    content: '';
    display: block;
    width: 60px;
    height: 4px;
    background: var(--accent-color);
    margin: var(--spacing-sm) auto 0;
    border-radius: var(--radius-full);
}

.section-description {
    text-align: center;
    color: var(--text-secondary);
    max-width: 700px;
    margin: 0 auto var(--spacing-md);
    font-size: var(--fs-lg);
}

.subsection-title {
    margin-top: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
    color: var(--primary-color);
}

.text-link {
    color: var(--primary-color);
    text-decoration: underline;
    text-decoration-color: var(--primary-light);
    text-underline-offset: 2px;
    transition: all var(--transition-fast);
}

.text-link:hover {
    text-decoration-color: var(--primary-dark);
}

/* ===================================
   Buttons
   =================================== */
.button {
    display: inline-block;
    padding: 0.875rem 2rem;
    font-size: var(--fs-base);
    font-weight: 500;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
    border: 2px solid transparent;
    text-align: center;
}

.button-primary {
    background: var(--accent-color);
    color: var(--text-white);
    border-color: var(--accent-color);
}

.button-primary:hover {
    background: var(--accent-hover);
    border-color: var(--accent-hover);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.button-secondary {
    background: transparent;
    color: var(--primary-color);
    border-color: var(--primary-color);
}

.button-secondary:hover {
    background: var(--primary-color);
    color: var(--text-white);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

/* ===================================
   Header & Navigation
   =================================== */
.header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background: var(--bg-primary);
    box-shadow: var(--shadow-sm);
    z-index: 1000;
    transition: all var(--transition-base);
}

.header.scrolled {
    box-shadow: var(--shadow-md);
}

.nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: var(--header-height);
}

.nav-logo {
    font-size: var(--fs-lg);
    font-weight: 600;
    color: var(--primary-color);
}

.nav-logo:hover {
    color: var(--primary-dark);
}

.nav-list {
    display: flex;
    list-style: none;
    gap: var(--spacing-md);
}

.nav-link {
    font-weight: 500;
    color: var(--text-primary);
    padding: 0.5rem 1rem;
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.nav-link:hover,
.nav-link.active {
    color: var(--primary-color);
    background: var(--bg-secondary);
}

/* Mobile Menu */
.nav-toggle {
    display: none;
    flex-direction: column;
    gap: 4px;
    cursor: pointer;
}

.nav-toggle span {
    display: block;
    width: 25px;
    height: 3px;
    background: var(--primary-color);
    border-radius: var(--radius-full);
    transition: all var(--transition-base);
}

.nav-close {
    display: none;
    position: absolute;
    top: 1rem;
    right: 1rem;
    font-size: 2rem;
    color: var(--text-primary);
    cursor: pointer;
}

/* ===================================
   Hero Section
   =================================== */
.hero {
    padding-top: calc(var(--header-height) + var(--spacing-xl));
    padding-bottom: var(--spacing-xl);
    background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-primary) 100%);
}

.hero-container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-lg);
    align-items: center;
}

.hero-content {
    order: 1;
}

.hero-title {
    margin-bottom: var(--spacing-xs);
    color: var(--primary-color);
}

.hero-subtitle {
    font-size: var(--fs-xl);
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    font-weight: 500;
}

.hero-description {
    font-size: var(--fs-lg);
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    line-height: var(--lh-loose);
}

.hero-buttons {
    display: flex;
    gap: var(--spacing-sm);
    flex-wrap: wrap;
}

.hero-image {
    order: 2;
    display: flex;
    justify-content: center;
}

.hero-image-wrapper {
    width: 100%;
    max-width: 400px;
    aspect-ratio: 1;
    border-radius: var(--radius-xl);
    overflow: hidden;
    box-shadow: var(--shadow-xl);
    border: 4px solid var(--bg-primary);
}

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

/* ===================================
   About Section
   =================================== */
.about {
    background: var(--bg-primary);
}

.about-content {
    max-width: 900px;
    margin: 0 auto;
}

.about-text {
    margin-bottom: var(--spacing-lg);
}

.about-description {
    font-size: var(--fs-lg);
    color: var(--text-secondary);
    text-align: center;
}

/* Statistics Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.stat-card {
    background: var(--bg-secondary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    text-align: center;
    border: 2px solid var(--border-light);
    transition: all var(--transition-base);
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
    border-color: var(--primary-light);
}

.stat-number {
    font-size: var(--fs-4xl);
    color: var(--primary-color);
    margin-bottom: var(--spacing-xs);
    font-weight: 700;
}

.stat-label {
    color: var(--text-secondary);
    font-size: var(--fs-base);
    margin: 0;
}

/* Education */
.education {
    margin-top: var(--spacing-lg);
}

.education-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-md);
}

.education-card {
    background: var(--bg-secondary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    border-left: 4px solid var(--primary-color);
}

.education-degree {
    font-weight: 600;
    font-size: var(--fs-lg);
    color: var(--primary-color);
    margin-bottom: var(--spacing-xs);
}

.education-school {
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
}

.education-year {
    color: var(--text-secondary);
    font-size: var(--fs-sm);
}

/* ===================================
   Research & Experience Section
   =================================== */
.research {
    background: var(--bg-secondary);
}

/* Current Position */
.current-position {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    margin-bottom: var(--spacing-lg);
    color: var(--text-white);
}

.position-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-xs);
}

.position-title {
    color: var(--text-white);
    margin: 0;
}

.position-badge {
    background: var(--accent-color);
    color: var(--text-white);
    padding: 0.25rem 0.75rem;
    border-radius: var(--radius-full);
    font-size: var(--fs-sm);
    font-weight: 600;
}

.position-org {
    font-size: var(--fs-lg);
    margin-bottom: var(--spacing-sm);
    opacity: 0.9;
}

.position-description {
    margin: 0;
    opacity: 0.9;
}

/* Timeline */
.timeline {
    position: relative;
    padding-left: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

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

.timeline-item {
    position: relative;
    padding-bottom: var(--spacing-lg);
}

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

.timeline-marker {
    position: absolute;
    left: -34px;
    top: 0;
    width: 12px;
    height: 12px;
    border-radius: var(--radius-full);
    background: var(--primary-color);
    border: 3px solid var(--bg-secondary);
}

.timeline-content {
    background: var(--bg-primary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

.timeline-content:hover {
    box-shadow: var(--shadow-md);
    transform: translateX(4px);
}

.timeline-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: var(--spacing-sm);
    flex-wrap: wrap;
    margin-bottom: var(--spacing-xs);
}

.timeline-title {
    color: var(--primary-color);
    flex: 1;
    margin: 0;
}

.timeline-date {
    color: var(--text-secondary);
    font-size: var(--fs-sm);
    white-space: nowrap;
}

.timeline-org {
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: 0.25rem;
}

.timeline-location {
    color: var(--text-secondary);
    font-size: var(--fs-sm);
    margin-bottom: var(--spacing-sm);
}

.timeline-achievements {
    list-style: none;
    padding-left: 0;
}

.timeline-achievements li {
    position: relative;
    padding-left: 1.5rem;
    margin-bottom: 0.5rem;
    color: var(--text-secondary);
}

.timeline-achievements li::before {
    content: '▸';
    position: absolute;
    left: 0;
    color: var(--accent-color);
    font-weight: bold;
}

/* Skills Grid */
.skills-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-md);
}

.skill-card {
    background: var(--bg-primary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

.skill-card:hover {
    box-shadow: var(--shadow-md);
    transform: translateY(-4px);
}

.skill-title {
    color: var(--primary-color);
    margin-bottom: var(--spacing-sm);
    font-size: var(--fs-xl);
}

.skill-list {
    list-style: none;
    padding-left: 0;
}

.skill-list li {
    position: relative;
    padding-left: 1.5rem;
    margin-bottom: 0.5rem;
    color: var(--text-secondary);
}

.skill-list li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--accent-color);
    font-weight: bold;
}

/* ===================================
   Publications Section
   =================================== */
.publications {
    background: var(--bg-primary);
}

.publications-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.publication-card {
    background: var(--bg-secondary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    border-top: 4px solid var(--primary-color);
    transition: all var(--transition-base);
    display: flex;
    flex-direction: column;
}

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

.publication-journal {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    border-radius: var(--radius-full);
    font-size: var(--fs-xs);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    margin-bottom: var(--spacing-sm);
    width: fit-content;
}

.publication-journal.nature {
    background: #d32f2f;
    color: var(--text-white);
}

.publication-journal.nature-genetics {
    background: #1976d2;
    color: var(--text-white);
}

.publication-journal.nature-immunology {
    background: #388e3c;
    color: var(--text-white);
}

.publication-journal.science {
    background: #512da8;
    color: var(--text-white);
}

.publication-journal.cell-reports {
    background: #f57c00;
    color: var(--text-white);
}

.publication-year {
    color: var(--text-secondary);
    font-size: var(--fs-sm);
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
}

.publication-title {
    font-size: var(--fs-lg);
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
    line-height: var(--lh-tight);
}

.publication-authors {
    color: var(--text-secondary);
    font-size: var(--fs-sm);
    margin-bottom: var(--spacing-sm);
    flex-grow: 1;
}

.publication-link {
    color: var(--primary-color);
    font-weight: 500;
    display: inline-flex;
    align-items: center;
    gap: 0.25rem;
    transition: all var(--transition-fast);
}

.publication-link:hover {
    color: var(--primary-dark);
    gap: 0.5rem;
}

.publications-footer {
    text-align: center;
    padding-top: var(--spacing-md);
    border-top: 2px solid var(--border-light);
}

.publications-note {
    font-size: var(--fs-lg);
    color: var(--text-secondary);
}

/* ===================================
   Contact Section
   =================================== */
.contact {
    background: var(--bg-secondary);
}

.contact-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    max-width: 900px;
    margin: 0 auto;
}

.contact-info {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.contact-item {
    display: flex;
    gap: var(--spacing-sm);
    background: var(--bg-primary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

.contact-item:hover {
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
}

.contact-icon {
    flex-shrink: 0;
    width: 48px;
    height: 48px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--primary-light);
    color: var(--text-white);
    border-radius: var(--radius-md);
}

.contact-details {
    flex: 1;
}

.contact-label {
    font-size: var(--fs-sm);
    color: var(--text-secondary);
    font-weight: 500;
    margin-bottom: 0.25rem;
}

.contact-value {
    font-size: var(--fs-lg);
    color: var(--primary-color);
    font-weight: 500;
}

.contact-value:hover {
    color: var(--primary-dark);
}

/* Social Links */
.social-links {
    background: var(--bg-primary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
}

.social-title {
    color: var(--primary-color);
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.social-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--spacing-sm);
}

.social-link {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-sm);
    background: var(--bg-secondary);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-weight: 500;
    transition: all var(--transition-base);
}

.social-link:hover {
    background: var(--primary-color);
    color: var(--text-white);
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

.social-link svg {
    width: 20px;
    height: 20px;
}

/* ===================================
   Footer
   =================================== */
.footer {
    background: var(--bg-dark);
    color: var(--text-white);
    padding: var(--spacing-md) 0;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
}

.footer-text {
    color: var(--text-white);
    opacity: 0.8;
    margin: 0;
}

.footer-links {
    display: flex;
    gap: var(--spacing-sm);
    align-items: center;
    margin: 0;
}

.footer-link {
    color: var(--text-white);
    opacity: 0.8;
    transition: opacity var(--transition-fast);
}

.footer-link:hover {
    opacity: 1;
}

.footer-separator {
    color: var(--text-white);
    opacity: 0.4;
}

/* ===================================
   Back to Top Button
   =================================== */
.back-to-top {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 50px;
    height: 50px;
    background: var(--primary-color);
    color: var(--text-white);
    border: none;
    border-radius: var(--radius-full);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow-lg);
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-base);
    z-index: 999;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}

.back-to-top:hover {
    background: var(--primary-dark);
    transform: translateY(-4px);
}

/* ===================================
   Animations
   =================================== */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeInUp 0.6s ease-out;
}

/* Scroll animations (applied via JavaScript) */
.scroll-reveal {
    opacity: 0;
    transform: translateY(30px);
    transition: all 0.6s ease-out;
}

.scroll-reveal.revealed {
    opacity: 1;
    transform: translateY(0);
}

/* ===================================
   Selection Styles
   =================================== */
::selection {
    background: var(--primary-light);
    color: var(--text-white);
}

::-moz-selection {
    background: var(--primary-light);
    color: var(--text-white);
}

/* ===================================
   Focus Styles for Accessibility
   =================================== */
:focus-visible {
    outline: 2px solid var(--accent-color);
    outline-offset: 2px;
}

button:focus-visible,
a:focus-visible {
    outline: 2px solid var(--accent-color);
    outline-offset: 2px;
}