/* ============================================
   Academic Personal Website - Stylesheet
   Minimalist, Modern, Academic Design
   ============================================ */

/* --------------------------------------------
   CSS Variables & Reset
   -------------------------------------------- */
:root {
    /* Colors */
    --color-bg: #ffffff;
    --color-bg-secondary: #f9fafb;
    --color-text-primary: #1a1a1a;
    --color-text-secondary: #4a4a4a;
    --color-text-muted: #6b7280;
    --color-accent: #1e40af;
    --color-accent-light: #3b82f6;
    --color-accent-hover: #1e3a8a;
    --color-border: #e5e7eb;
    --color-shadow: rgba(0, 0, 0, 0.1);
    
    /* Typography */
    --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-mono: 'SF Mono', Monaco, 'Cascadia Code', 'Roboto Mono', Consolas, monospace;
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-2xl: 4rem;
    
    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-normal: 250ms ease;
    --transition-slow: 350ms ease;
    
    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    scroll-snap-type: y mandatory;
    font-size: 16px;
}

body {
    font-family: var(--font-sans);
    color: var(--color-text-primary);
    background-color: var(--color-bg);
    line-height: 1.7;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    overflow-x: hidden;
}

body {
    font-family: var(--font-sans);
    color: var(--color-text-primary);
    background-color: var(--color-bg);
    line-height: 1.7;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

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

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

/* --------------------------------------------
   Container & Layout
   -------------------------------------------- */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

.section {
    padding: var(--spacing-2xl) 0;
}

.section-title {
    font-size: 2rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: var(--spacing-xl);
    color: var(--color-text-primary);
    letter-spacing: -0.02em;
}

/* --------------------------------------------
   Navigation Bar (Sticky)
   -------------------------------------------- */
.navbar {
    position: sticky;
    top: 0;
    z-index: 1000;
    background-color: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--color-border);
    transition: box-shadow var(--transition-normal);
}

.navbar.scrolled {
    box-shadow: 0 1px 3px var(--color-shadow);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 64px;
}

.nav-logo {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--color-text-primary);
    transition: color var(--transition-fast);
}

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

.nav-menu {
    display: flex;
    list-style: none;
    gap: var(--spacing-lg);
    align-items: center;
}

.nav-link {
    font-size: 0.95rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    padding: var(--spacing-xs) 0;
    position: relative;
    transition: color var(--transition-fast);
}

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

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

.nav-link:hover::after {
    width: 100%;
}

/* Hamburger Menu (Hidden on desktop, visible on mobile) */
.hamburger {
    display: none;
    flex-direction: column;
    cursor: pointer;
    gap: 4px;
    padding: var(--spacing-xs);
    border-radius: var(--radius-sm);
    transition: background-color var(--transition-fast);
}

.hamburger:hover {
    background-color: var(--color-bg-secondary);
}

.bar {
    width: 24px;
    height: 2px;
    background-color: var(--color-text-primary);
    transition: all var(--transition-fast);
}

/* --------------------------------------------
   Home / About Section
   -------------------------------------------- */
.home-section {
    min-height: 100vh;
    display: flex;
    align-items: center;
    background: linear-gradient(135deg, var(--color-bg) 0%, var(--color-bg-secondary) 100%);
    scroll-snap-align: start;
}

.section-inner {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
    width: 100%;
}

.section-footer {
    text-align: center;
    padding-top: var(--spacing-xl);
    margin-top: auto;
}

.section-footer-link {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-xs);
    font-size: 0.9rem;
    color: var(--color-accent);
    font-weight: 500;
    transition: all var(--transition-fast);
}

.section-footer-link:hover {
    color: var(--color-accent-hover);
    gap: calc(var(--spacing-xs) + 4px);
}

.section-footer-link svg {
    width: 16px;
    height: 16px;
}

.home-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-2xl);
    align-items: center;
}

.home-title {
    font-size: 3.5rem;
    font-weight: 700;
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-sm);
    letter-spacing: -0.03em;
    line-height: 1.1;
}

.home-subtitle {
    font-size: 1.25rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-md);
    font-weight: 400;
}

.home-intro {
    font-size: 1.05rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-lg);
    max-width: 540px;
}

.home-links {
    display: flex;
    gap: var(--spacing-sm);
}

.home-image {
    display: flex;
    justify-content: center;
    align-items: center;
}

.profile-placeholder {
    width: 280px;
    height: 280px;
    border-radius: var(--radius-lg);
    background-color: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: hidden;
    transition: transform var(--transition-normal), box-shadow var(--transition-normal);
}

.profile-placeholder:hover {
    transform: translateY(-4px);
    box-shadow: 0 12px 24px var(--color-shadow);
}

.profile-placeholder svg {
    width: 60%;
    height: 60%;
    opacity: 0.5;
}

/* --------------------------------------------
   Buttons
   -------------------------------------------- */
.btn {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-sm) var(--spacing-lg);
    font-size: 0.95rem;
    font-weight: 500;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
    cursor: pointer;
    border: none;
}

.btn-primary {
    background-color: var(--color-accent);
    color: white;
}

.btn-primary:hover {
    background-color: var(--color-accent-hover);
    color: white;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(30, 64, 175, 0.3);
}

.btn-secondary {
    background-color: transparent;
    color: var(--color-text-primary);
    border: 1px solid var(--color-border);
}

.btn-secondary:hover {
    background-color: var(--color-bg-secondary);
    border-color: var(--color-text-muted);
    transform: translateY(-2px);
}

.btn-icon {
    width: 18px;
    height: 18px;
}

/* --------------------------------------------
   Research Section
   -------------------------------------------- */
.research-section {
    background-color: var(--color-bg);
    min-height: 100vh;
    scroll-snap-align: start;
}

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

.research-card {
    padding: var(--spacing-lg);
    background-color: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-normal);
    cursor: default;
}

.research-card:hover {
    transform: translateY(-6px);
    box-shadow: 0 12px 24px var(--color-shadow);
    border-color: var(--color-accent-light);
}

.research-icon {
    width: 48px;
    height: 48px;
    margin-bottom: var(--spacing-md);
    color: var(--color-accent);
}

.research-icon svg {
    width: 100%;
    height: 100%;
}

.research-title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-sm);
    letter-spacing: -0.01em;
}

.research-description {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
}

/* --------------------------------------------
   Publications Section
   -------------------------------------------- */
.publications-section {
    background-color: var(--color-bg-secondary);
    min-height: 100vh;
    scroll-snap-align: start;
}

.publications-year {
    margin-bottom: var(--spacing-xl);
}

.year-title {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-xs);
    border-bottom: 2px solid var(--color-border);
    display: inline-block;
}

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

.publication-item {
    padding: var(--spacing-md);
    background-color: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-normal);
}

.publication-item:hover {
    transform: translateY(-3px);
    box-shadow: 0 8px 16px var(--color-shadow);
    border-color: var(--color-accent-light);
}

.publication-title {
    font-size: 1.05rem;
    font-weight: 500;
    margin-bottom: var(--spacing-xs);
}

.pub-link {
    color: var(--color-text-primary);
    transition: color var(--transition-fast);
}

.pub-link:hover {
    color: var(--color-accent);
}

.publication-authors {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xs);
}

.publication-venue {
    font-size: 0.9rem;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-sm);
}

.publication-links {
    display: flex;
    gap: var(--spacing-sm);
}

.pub-link-small {
    font-size: 0.85rem;
    color: var(--color-accent);
    padding: 2px 8px;
    background-color: rgba(59, 130, 246, 0.1);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.pub-link-small:hover {
    background-color: rgba(59, 130, 246, 0.2);
    color: var(--color-accent-hover);
}

/* --------------------------------------------
   CV Section
   -------------------------------------------- */
.cv-section {
    background-color: var(--color-bg);
    min-height: 100vh;
    scroll-snap-align: start;
}

.cv-content {
    max-width: 900px;
    margin: 0 auto var(--spacing-xl);
}

.cv-category {
    margin-bottom: var(--spacing-xl);
}

.cv-category-title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-xs);
    border-bottom: 2px solid var(--color-accent);
    display: inline-block;
}

.cv-item {
    margin-bottom: var(--spacing-md);
    padding: var(--spacing-md);
    border-left: 3px solid var(--color-border);
    transition: all var(--transition-fast);
}

.cv-item:hover {
    border-left-color: var(--color-accent);
    background-color: var(--color-bg-secondary);
    padding-left: calc(var(--spacing-md) + 4px);
}

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

.cv-item-title {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--color-text-primary);
}

.cv-item-year {
    font-size: 0.9rem;
    color: var(--color-text-muted);
    font-weight: 500;
}

.cv-item-details {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
}

.cv-item-note {
    font-size: 0.9rem;
    color: var(--color-text-muted);
    font-style: italic;
}

.cv-download {
    text-align: center;
    margin-top: var(--spacing-xl);
}

/* --------------------------------------------
   Contact Section
   -------------------------------------------- */
.contact-section {
    background-color: var(--color-bg-secondary);
    min-height: 100vh;
    scroll-snap-align: start;
}

.contact-content {
    max-width: 700px;
    margin: 0 auto;
}

.contact-text {
    font-size: 1.05rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-lg);
    text-align: center;
}

.contact-links {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-xl);
}

.contact-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    background-color: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.contact-item:hover {
    border-color: var(--color-accent-light);
    transform: translateX(4px);
}

.contact-icon {
    width: 20px;
    height: 20px;
    color: var(--color-accent);
    flex-shrink: 0;
}

.contact-link {
    font-size: 1rem;
    color: var(--color-text-primary);
    transition: color var(--transition-fast);
}

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

.contact-academic {
    text-align: center;
    padding-top: var(--spacing-lg);
    border-top: 1px solid var(--color-border);
}

.academic-title {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--color-text-muted);
    margin-bottom: var(--spacing-sm);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.academic-links {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
}

.academic-link {
    font-size: 0.95rem;
    color: var(--color-accent);
    transition: color var(--transition-fast);
}

.academic-link:hover {
    color: var(--color-accent-hover);
    text-decoration: underline;
}

.separator {
    color: var(--color-border);
}

/* --------------------------------------------
   Footer
   -------------------------------------------- */
.footer {
    background-color: var(--color-bg);
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-lg) 0;
}

.footer-text {
    text-align: center;
    font-size: 0.9rem;
    color: var(--color-text-muted);
}

/* --------------------------------------------
   Fade-in Animation (Scroll-triggered)
   -------------------------------------------- */
.fade-in {
    opacity: 0;
    transform: translateY(30px);
    transition: opacity var(--transition-slow), transform var(--transition-slow);
}

.fade-in.visible {
    opacity: 1;
    transform: translateY(0);
}

/* Staggered animation for cards */
.research-card.fade-in:nth-child(2) { transition-delay: 50ms; }
.research-card.fade-in:nth-child(3) { transition-delay: 100ms; }
.research-card.fade-in:nth-child(4) { transition-delay: 150ms; }
.research-card.fade-in:nth-child(5) { transition-delay: 200ms; }

.publications-year.fade-in:nth-child(2) { transition-delay: 100ms; }
.publications-year.fade-in:nth-child(3) { transition-delay: 200ms; }
.publications-year.fade-in:nth-child(4) { transition-delay: 300ms; }

/* --------------------------------------------
   Page Load Animation
   -------------------------------------------- */
@keyframes pageLoad {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

body {
    animation: pageLoad 400ms ease-out;
}

/* --------------------------------------------
   Responsive Design
   -------------------------------------------- */
@media (max-width: 992px) {
    .home-content {
        grid-template-columns: 1fr;
        text-align: center;
    }
    
    .home-text {
        order: 2;
    }
    
    .home-image {
        order: 1;
    }
    
    .home-title {
        font-size: 2.5rem;
    }
    
    .home-links {
        justify-content: center;
    }
    
    .research-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 768px) {
    :root {
        --spacing-2xl: 3rem;
        --spacing-xl: 2rem;
    }
    
    .nav-menu {
        position: fixed;
        top: 64px;
        left: 0;
        right: 0;
        background-color: var(--color-bg);
        flex-direction: column;
        padding: var(--spacing-lg);
        gap: var(--spacing-md);
        border-bottom: 1px solid var(--color-border);
        box-shadow: 0 4px 12px var(--color-shadow);
        transform: translateY(-100%);
        opacity: 0;
        visibility: hidden;
        transition: all var(--transition-normal);
    }
    
    .nav-menu.active {
        transform: translateY(0);
        opacity: 1;
        visibility: visible;
    }
    
    .hamburger {
        display: flex;
    }
    
    .hamburger.active .bar:nth-child(1) {
        transform: translateY(6px) rotate(45deg);
    }
    
    .hamburger.active .bar:nth-child(2) {
        opacity: 0;
    }
    
    .hamburger.active .bar:nth-child(3) {
        transform: translateY(-6px) rotate(-45deg);
    }
    
    .home-title {
        font-size: 2rem;
    }
    
    .home-subtitle {
        font-size: 1.1rem;
    }
    
    .section-title {
        font-size: 1.75rem;
    }
    
    .cv-item-header {
        flex-direction: column;
    }
    
    .academic-links {
        flex-direction: column;
        gap: var(--spacing-xs);
    }
    
    .separator {
        display: none;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 var(--spacing-md);
    }
    
    .home-title {
        font-size: 1.75rem;
    }
    
    .home-links {
        flex-direction: column;
        width: 100%;
    }
    
    .btn {
        width: 100%;
        justify-content: center;
    }
    
    .profile-placeholder {
        width: 200px;
        height: 200px;
    }
}

/* --------------------------------------------
   Print Styles
   -------------------------------------------- */
@media print {
    .navbar,
    .hamburger,
    .btn,
    .publication-links,
    .cv-download {
        display: none;
    }
    
    .section {
        padding: 20px 0;
    }
    
    a {
        color: var(--color-text-primary);
        text-decoration: underline;
    }
}