/* CSS Variables - Light Theme */
:root {
    --color-primary: #0f172a;
    --color-primary-light: #1e293b;
    --color-accent: #2563eb;
    --color-accent-hover: #1d4ed8;
    --color-text: #0f172a;
    --color-text-secondary: #475569;
    --color-text-muted: #64748b;
    --color-bg: #ffffff;
    --color-bg-alt: #f8fafc;
    --color-bg-card: #ffffff;
    --color-border: #e2e8f0;
    --color-border-light: #f1f5f9;
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-serif: 'Source Serif 4', Georgia, 'Times New Roman', serif;
    --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.04);
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -1px rgba(0, 0, 0, 0.04);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -2px rgba(0, 0, 0, 0.04);
    --radius-sm: 6px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --transition-fast: 150ms ease;
    --transition: 200ms ease;
    --transition-slow: 300ms ease;
}

/* Dark Theme */
[data-theme="dark"] {
    --color-primary: #f1f5f9;
    --color-primary-light: #e2e8f0;
    --color-accent: #60a5fa;
    --color-accent-hover: #93c5fd;
    --color-text: #f1f5f9;
    --color-text-secondary: #cbd5e1;
    --color-text-muted: #94a3b8;
    --color-bg: #0f172a;
    --color-bg-alt: #1e293b;
    --color-bg-card: #1e293b;
    --color-border: #334155;
    --color-border-light: #1e293b;
    --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.2);
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3), 0 1px 2px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.3), 0 2px 4px -1px rgba(0, 0, 0, 0.2);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4), 0 4px 6px -2px rgba(0, 0, 0, 0.2);
}

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

html {
    scroll-behavior: smooth;
    font-size: 17px;
}

body {
    font-family: var(--font-sans);
    font-size: 1rem;
    line-height: 1.7;
    color: var(--color-text);
    background-color: var(--color-bg);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    transition: background-color var(--transition-slow), color var(--transition-slow);
}

/* Container */
.container {
    max-width: 860px;
    margin: 0 auto;
    padding: 0 2rem;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: 600;
    line-height: 1.3;
    color: var(--color-primary);
    letter-spacing: -0.01em;
}

h1 {
    font-size: 2.25rem;
    font-weight: 700;
    letter-spacing: -0.03em;
}

h2 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 2.5rem;
    color: var(--color-text);
    position: relative;
    display: inline-block;
}

h2::after {
    content: '';
    position: absolute;
    bottom: -8px;
    left: 0;
    width: 40px;
    height: 3px;
    background: var(--color-accent);
    border-radius: 2px;
}

h3 {
    font-size: 1.15rem;
    font-weight: 700;
    margin-bottom: 1.5rem;
    color: var(--color-accent);
    text-transform: uppercase;
    letter-spacing: 0.12em;
    padding-bottom: 0.75rem;
    border-bottom: 2px solid var(--color-border);
}

h4 {
    font-size: 1.05rem;
    font-weight: 500;
    color: var(--color-text);
}

p {
    margin-bottom: 1rem;
}

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

a:hover {
    color: var(--color-accent-hover);
}

strong {
    font-weight: 600;
}

/* Navigation */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    background: var(--color-bg);
    border-bottom: 1px solid transparent;
    transition: all var(--transition);
}

.navbar.scrolled {
    background: var(--color-bg);
    border-bottom-color: var(--color-border);
    box-shadow: var(--shadow-sm);
}

[data-theme="dark"] .navbar {
    background: rgba(15, 23, 42, 0.9);
    backdrop-filter: blur(12px);
}

[data-theme="dark"] .navbar.scrolled {
    background: rgba(15, 23, 42, 0.95);
}

.nav-container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 64px;
}

.nav-logo {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--color-primary);
    letter-spacing: -0.01em;
}

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

.nav-menu {
    display: flex;
    list-style: none;
    gap: 0.5rem;
    align-items: center;
}

.nav-menu a {
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    padding: 0.5rem 0.875rem;
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.nav-menu a:hover {
    color: var(--color-text);
    background: var(--color-bg-alt);
}

.nav-cv {
    background: var(--color-primary) !important;
    color: var(--color-bg) !important;
    margin-left: 0.5rem;
}

.nav-cv:hover {
    opacity: 0.9;
    background: var(--color-primary-light) !important;
}

/* Theme Toggle */
.theme-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    background: var(--color-bg-alt);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    margin-left: 0.75rem;
    transition: all var(--transition-fast);
}

.theme-toggle:hover {
    background: var(--color-border);
}

.theme-toggle svg {
    width: 18px;
    height: 18px;
    color: var(--color-text-secondary);
}

.theme-toggle .sun-icon {
    display: none;
}

[data-theme="dark"] .theme-toggle .sun-icon {
    display: block;
}

[data-theme="dark"] .theme-toggle .moon-icon {
    display: none;
}

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

.nav-toggle span {
    width: 22px;
    height: 2px;
    background: var(--color-text);
    border-radius: 1px;
    transition: var(--transition);
}

/* Hero Section */
.hero {
    padding: 140px 0 100px;
    background: var(--color-bg);
}

.hero-container {
    max-width: 860px;
    margin: 0 auto;
    padding: 0 2rem;
}

.hero-grid {
    display: grid;
    grid-template-columns: 260px 1fr;
    gap: 3.5rem;
    align-items: start;
}

.hero-photo {
    position: relative;
}

.hero-photo img {
    width: 100%;
    height: auto;
    aspect-ratio: 1;
    object-fit: cover;
    border-radius: 50%;
    box-shadow: var(--shadow-md);
    transition: transform var(--transition), box-shadow var(--transition);
}

.hero-photo img:hover {
    transform: scale(1.02);
    box-shadow: var(--shadow-lg);
}

.hero-content {
    padding-top: 0.5rem;
}

.hero h1 {
    margin-bottom: 0.35rem;
    font-family: var(--font-serif);
    font-weight: 600;
    letter-spacing: -0.01em;
    color: var(--color-primary);
}

.hero-title {
    font-size: 1.05rem;
    color: var(--color-text-secondary);
    margin-bottom: 0.15rem;
    font-weight: 500;
    letter-spacing: 0.01em;
}

.hero-institution {
    font-size: 0.9rem;
    margin-bottom: 1.25rem;
}

.hero-institution a {
    color: var(--color-text-muted);
    border-bottom: 1px solid transparent;
}

.hero-institution a:hover {
    color: var(--color-accent);
    border-bottom-color: var(--color-accent);
}

.hero-bio {
    font-family: var(--font-serif);
    font-size: 1.05rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
    margin-bottom: 1.5rem;
}

.hero-bio strong {
    color: var(--color-text);
    font-weight: 500;
}

.hero-links {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    align-items: center;
}

.social-link {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 38px;
    height: 38px;
    padding: 0;
    background: var(--color-bg-alt);
    border: 1px solid var(--color-border);
    border-radius: 50%;
    font-size: 0.8rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
}

.social-link:hover {
    border-color: var(--color-accent);
    color: var(--color-accent);
    background: var(--color-bg);
    transform: translateY(-2px);
}

.social-link .icon {
    width: 1.1rem;
    height: 1.1rem;
    flex-shrink: 0;
}

.social-link.text-link {
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.02em;
}

/* Main Content Sections */
section {
    padding: 5rem 0;
}

section:nth-child(even) {
    background: var(--color-bg-alt);
}

/* Research Section */
.research-category {
    margin-bottom: 3.5rem;
}

.research-category:last-child {
    margin-bottom: 0;
}

.paper {
    padding: 1.5rem 0;
    border-bottom: 1px solid var(--color-border-light);
}

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

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

.paper h4 {
    font-family: var(--font-serif);
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: 0.4rem;
    line-height: 1.45;
}

.paper h4 a {
    color: var(--color-text);
    text-decoration: none;
    background-image: linear-gradient(var(--color-accent), var(--color-accent));
    background-size: 0% 2px;
    background-position: 0 100%;
    background-repeat: no-repeat;
    transition: background-size 0.3s ease, color 0.2s ease;
}

.paper h4 a:hover {
    color: var(--color-accent);
    background-size: 100% 2px;
}

.paper .authors {
    font-size: 0.95rem;
    color: var(--color-text-muted);
    margin-bottom: 0.3rem;
}

.paper .authors a {
    color: var(--color-text-muted);
    border-bottom: 1px dotted var(--color-border);
}

.paper .authors a:hover {
    color: var(--color-accent);
    border-bottom-color: var(--color-accent);
}

.paper .venue {
    font-size: 0.95rem;
    margin-bottom: 0.6rem;
}

.paper .venue em {
    font-style: normal;
    color: var(--color-text-secondary);
    font-weight: 700;
}

.paper .conferences {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    margin-bottom: 0.6rem;
}

.paper .conferences::before {
    content: "Conferences: ";
    font-weight: 500;
    color: var(--color-text-secondary);
}

.paper .award {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    font-style: italic;
    margin-bottom: 0.6rem;
}

.paper-links {
    display: flex;
    flex-wrap: wrap;
    gap: 0.4rem;
    margin-top: 0.75rem;
}

.paper-links a {
    display: inline-block;
    padding: 0.3rem 0.625rem;
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    font-weight: 500;
    color: var(--color-text-muted);
    transition: all var(--transition-fast);
}

.paper-links a:hover {
    background: var(--color-accent);
    border-color: var(--color-accent);
    color: white;
}

/* Abstract Toggle Button */
.abstract-toggle {
    display: inline-block;
    padding: 0.3rem 0.625rem;
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    font-weight: 500;
    color: var(--color-text-muted);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.abstract-toggle:hover {
    background: var(--color-accent);
    border-color: var(--color-accent);
    color: white;
}

.abstract-toggle.active {
    background: var(--color-bg-alt);
    border-color: var(--color-accent);
    color: var(--color-accent);
}

/* Abstract Content */
.abstract-content {
    display: none;
    margin-top: 0.75rem;
    padding: 1rem 1.25rem;
    background: var(--color-bg-alt);
    border-left: 3px solid var(--color-accent);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
    font-size: 0.9rem;
    line-height: 1.7;
    color: var(--color-text-secondary);
}

.abstract-content.show {
    display: block;
}

.abstract-content p {
    margin-bottom: 0;
}

/* Discussions Section */
.discussions-grid {
    display: grid;
    gap: 0.75rem;
}

.discussion-item {
    background: var(--color-bg-card);
    padding: 1.25rem 1.5rem;
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border);
    transition: all var(--transition-fast);
}

.discussion-item:hover {
    border-color: var(--color-accent);
    box-shadow: var(--shadow-sm);
}

.discussion-item h4 {
    font-family: var(--font-serif);
    font-size: 1rem;
    font-weight: 500;
    color: var(--color-text);
    margin-bottom: 0.35rem;
    line-height: 1.4;
}

.discussion-authors {
    font-size: 0.9rem;
    color: var(--color-text-muted);
    margin-bottom: 0.2rem !important;
}

.discussion-venue {
    font-size: 0.85rem;
    color: var(--color-accent);
    font-weight: 500;
    margin-bottom: 0.6rem !important;
}

.discussion-link {
    display: inline-block;
    padding: 0.3rem 0.75rem;
    background: var(--color-primary);
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    font-weight: 500;
    color: var(--color-bg) !important;
    transition: all var(--transition-fast);
}

.discussion-link:hover {
    opacity: 0.9;
}

/* Teaching Section */
.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
    gap: 1.25rem;
    margin-bottom: 2.5rem;
}

.course-card {
    background: var(--color-bg-card);
    padding: 1.5rem;
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border);
    transition: all var(--transition-fast);
}

.course-card:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--color-accent);
    transform: translateY(-1px);
}

.course-card h4 {
    color: var(--color-text);
    margin-bottom: 0.5rem;
    font-size: 1rem;
}

.course-level {
    font-size: 0.85rem;
    color: var(--color-accent);
    font-weight: 500;
    margin-bottom: 0.2rem !important;
}

.course-term {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    margin-bottom: 0 !important;
}

.teaching-history {
    padding-top: 0.5rem;
}

.teaching-history h4 {
    color: var(--color-text-secondary);
    margin-bottom: 1rem;
    font-size: 0.95rem;
    font-weight: 500;
}

.teaching-history ul {
    list-style: none;
}

.teaching-history li {
    padding: 0.4rem 0;
    padding-left: 1.25rem;
    position: relative;
    color: var(--color-text-muted);
    font-size: 0.9rem;
}

.teaching-history li::before {
    content: '';
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 5px;
    height: 5px;
    border-radius: 50%;
    background: var(--color-accent);
}

/* Contact Section */
.contact-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 2rem;
}

.contact-item h4 {
    color: var(--color-text-muted);
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    margin-bottom: 0.5rem;
    font-weight: 600;
}

.contact-item p {
    color: var(--color-text-secondary);
    margin-bottom: 0;
    line-height: 1.6;
    font-size: 0.95rem;
}

.contact-item a {
    color: var(--color-text-secondary);
}

.contact-item a:hover {
    color: var(--color-accent);
}

/* Footer */
footer {
    padding: 2rem 0;
    text-align: center;
    border-top: 1px solid var(--color-border);
    background: var(--color-bg);
}

footer p {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    margin-bottom: 0;
}

/* Responsive Design */
@media (max-width: 768px) {
    html {
        font-size: 15px;
    }

    .container {
        padding: 0 1.5rem;
    }

    .nav-container {
        padding: 0 1.5rem;
    }

    .nav-menu {
        position: fixed;
        top: 64px;
        left: 0;
        right: 0;
        background: var(--color-bg);
        flex-direction: column;
        padding: 1rem;
        gap: 0;
        border-bottom: 1px solid var(--color-border);
        box-shadow: var(--shadow-lg);
        transform: translateY(-100%);
        opacity: 0;
        visibility: hidden;
        transition: all var(--transition);
    }

    .nav-menu.active {
        transform: translateY(0);
        opacity: 1;
        visibility: visible;
    }

    .nav-menu li {
        width: 100%;
    }

    .nav-menu a {
        display: block;
        padding: 0.75rem 1rem;
        border-radius: var(--radius-sm);
    }

    .nav-cv {
        text-align: center;
        margin: 0.5rem 0 0 0;
    }

    .theme-toggle {
        margin-left: 0.5rem;
    }

    .nav-toggle {
        display: flex;
    }

    .nav-toggle.active span:nth-child(1) {
        transform: rotate(45deg) translate(5px, 5px);
    }

    .nav-toggle.active span:nth-child(2) {
        opacity: 0;
    }

    .nav-toggle.active span:nth-child(3) {
        transform: rotate(-45deg) translate(5px, -5px);
    }

    h1 {
        font-size: 1.9rem;
    }

    h2 {
        font-size: 1.35rem;
    }

    .hero {
        padding: 120px 0 70px;
    }

    .hero-container {
        padding: 0 1.5rem;
    }

    .hero-grid {
        grid-template-columns: 1fr;
        gap: 2rem;
        text-align: center;
    }

    .hero-photo {
        max-width: 180px;
        margin: 0 auto;
    }

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

    .hero-content {
        text-align: left;
        padding-top: 0;
    }

    .hero-bio {
        font-size: 1.05rem;
    }

    section {
        padding: 4rem 0;
    }

    .paper h4 {
        font-size: 1rem;
    }

    .paper-links {
        gap: 0.35rem;
    }

    .paper-links a {
        padding: 0.25rem 0.5rem;
        font-size: 0.7rem;
    }

    .discussion-item {
        padding: 1rem 1.25rem;
    }

    .discussion-item h4 {
        font-size: 0.9rem;
    }

    .contact-grid {
        gap: 1.5rem;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 1.25rem;
    }

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

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

/* Print Styles */
@media print {
    .navbar,
    .nav-toggle,
    .theme-toggle {
        display: none !important;
    }

    .hero {
        padding-top: 2rem;
    }

    section {
        padding: 2rem 0;
    }

    a {
        color: var(--color-text);
    }

    .paper-links a {
        border: 1px solid var(--color-text-muted);
    }
}

/* Smooth transitions for theme changes */
* {
    transition: background-color var(--transition-slow),
                border-color var(--transition-slow),
                box-shadow var(--transition-slow);
}

a, button, .paper-links a, .social-link {
    transition: all var(--transition-fast);
}