/* ═══════════════════════════════════════════
   Yusong Han — Research Portfolio
   Editorial-scientific aesthetic
   ═══════════════════════════════════════════ */

/* ── Fonts ── */
@import url('https://fonts.googleapis.com/css2?family=DM+Serif+Display:ital@0;1&family=Source+Sans+3:wght@300;400;500;600&display=swap');

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

/* ── CSS Variables ── */
:root {
    --font-display: 'DM Serif Display', Georgia, serif;
    --font-body: 'Source Sans 3', -apple-system, system-ui, sans-serif;
    --font-mono: 'SF Mono', 'Fira Code', monospace;

    --bg: #fafaf7;
    --bg-card: #ffffff;
    --text: #1a1a1a;
    --text-secondary: #555;
    --text-tertiary: #888;
    --accent: #1a6b52;
    --accent-light: rgba(26, 107, 82, 0.08);
    --accent-hover: #145542;
    --border: #e8e5e0;
    --border-light: #f0ede8;
    --canvas-bg: rgb(30, 160, 120);
    --hero-text: #fff;
    --hero-text-secondary: rgba(255, 255, 255, 0.8);
    --shadow-sm: 0 1px 3px rgba(0,0,0,0.04);
    --shadow-md: 0 4px 20px rgba(0,0,0,0.06);
    --shadow-lg: 0 8px 40px rgba(0,0,0,0.08);
    --tag-bg: #f3f1ec;
    --tag-text: #444;
    --section-gap: 5rem;
}

.dark-mode {
    --bg: #0f1419;
    --bg-card: #161b22;
    --text: #e0e0e0;
    --text-secondary: #9da5b0;
    --text-tertiary: #6b7280;
    --accent: #3dd9a0;
    --accent-light: rgba(61, 217, 160, 0.08);
    --accent-hover: #5be8b5;
    --border: #21262d;
    --border-light: #1a1f26;
    --canvas-bg: rgb(30, 40, 55);
    --shadow-sm: 0 1px 3px rgba(0,0,0,0.2);
    --shadow-md: 0 4px 20px rgba(0,0,0,0.3);
    --shadow-lg: 0 8px 40px rgba(0,0,0,0.4);
    --tag-bg: #1c2330;
    --tag-text: #9da5b0;
}

/* ── Base ── */
html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-body);
    font-weight: 400;
    line-height: 1.7;
    color: var(--text);
    background-color: var(--bg);
    transition: background-color 0.4s, color 0.4s;
    -webkit-font-smoothing: antialiased;
}

a {
    color: var(--accent);
    text-decoration: none;
    transition: color 0.2s;
}
a:hover {
    color: var(--accent-hover);
}

/* ═══════════════════════════════════════════
   HERO SECTION
   ═══════════════════════════════════════════ */

#animation-container {
    width: 100%;
    height: 70vh;
    min-height: 480px;
    position: relative;
    background-color: var(--canvas-bg);
    overflow: hidden;
}

#animation-container canvas {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    opacity: 0;
    transition: opacity 0.6s ease;
}

#canvas-placeholder {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    background-color: var(--canvas-bg);
    transition: opacity 0.6s ease;
    z-index: 1;
}

.loading-spinner {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    z-index: 2;
}

.spinner {
    width: 36px;
    height: 36px;
    border: 3px solid rgba(255, 255, 255, 0.2);
    border-radius: 50%;
    border-top-color: rgba(255, 255, 255, 0.7);
    animation: spin 1s ease-in-out infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Hero overlay */
.hero-overlay {
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    z-index: 10;
    padding: 3rem 2rem;
    background: linear-gradient(to top,
        rgba(0, 0, 0, 0.55) 0%,
        rgba(0, 0, 0, 0.25) 60%,
        transparent 100%
    );
    pointer-events: none;
}

.hero-content {
    max-width: 1000px;
    margin: 0 auto;
    pointer-events: none;
}

.hero-content a {
    pointer-events: auto;
}

.hero-name {
    font-family: var(--font-display);
    font-size: 3.2rem;
    font-weight: 400;
    color: var(--hero-text);
    line-height: 1.15;
    letter-spacing: -0.01em;
    margin-bottom: 0.5rem;
}

.hero-tagline {
    font-size: 1.1rem;
    font-weight: 300;
    color: var(--hero-text-secondary);
    letter-spacing: 0.02em;
    margin-bottom: 0.3rem;
}

.hero-affiliation {
    font-size: 0.95rem;
    font-weight: 400;
    color: rgba(255, 255, 255, 0.6);
    margin-bottom: 1.2rem;
}

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

.hero-links a {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    color: rgba(255, 255, 255, 0.85);
    font-size: 0.9rem;
    font-weight: 400;
    padding: 0.35rem 0.7rem;
    border: 1px solid rgba(255, 255, 255, 0.25);
    border-radius: 4px;
    transition: all 0.25s;
    backdrop-filter: blur(4px);
    -webkit-backdrop-filter: blur(4px);
}

.hero-links a:hover {
    color: #fff;
    border-color: rgba(255, 255, 255, 0.6);
    background: rgba(255, 255, 255, 0.1);
}

.hero-links a i {
    font-size: 0.95rem;
}

/* (showcase band removed — merged into research cards) */

/* ═══════════════════════════════════════════
   MAIN CONTENT WRAPPER
   ═══════════════════════════════════════════ */

.page-content {
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 2rem;
}

/* ── Section styling ── */
.content-section {
    padding: var(--section-gap) 0;
    border-bottom: 1px solid var(--border-light);
}

.content-section:last-child {
    border-bottom: none;
}

.section-label {
    font-family: var(--font-mono);
    font-size: 0.72rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.15em;
    color: var(--accent);
    margin-bottom: 0.6rem;
}

.section-title {
    font-family: var(--font-display);
    font-size: 2rem;
    font-weight: 400;
    color: var(--text);
    line-height: 1.25;
    margin-bottom: 1.8rem;
}

/* ═══════════════════════════════════════════
   RESEARCH CARDS — dark panel style
   ═══════════════════════════════════════════ */

.research-card {
    display: grid;
    grid-template-columns: 1.2fr 1fr;
    gap: 0;
    align-items: stretch;
    margin-bottom: 2.5rem;
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: 10px;
    overflow: hidden;
    transition: opacity 0.6s ease, transform 0.6s ease, box-shadow 0.4s ease, border-color 0.4s ease;
    /* scroll animation */
    opacity: 0;
    transform: translateY(24px);
}

.research-card.visible {
    opacity: 1;
    transform: translateY(0);
}

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

.research-card:hover {
    box-shadow: 0 12px 48px rgba(0, 0, 0, 0.15);
}

.dark-mode .research-card:hover {
    box-shadow: 0 12px 48px rgba(0, 0, 0, 0.5);
}

.research-card:nth-child(even) {
    direction: rtl;
}
.research-card:nth-child(even) > * {
    direction: ltr;
}

/* Card variables — light mode */
:root {
    --card-bg: #ffffff;
    --card-border: #e2e0db;
    --card-text: #1a1a1a;
    --card-text-secondary: #555;
    --card-label-color: var(--accent);
    --card-label-bg: rgba(26, 107, 82, 0.08);
}

/* Card variables — dark mode */
.dark-mode {
    --card-bg: #0d1117;
    --card-border: #1c2230;
    --card-text: #e6edf3;
    --card-text-secondary: #8b949e;
    --card-label-color: #3dd9a0;
    --card-label-bg: rgba(61, 217, 160, 0.1);
}

.research-card-media {
    position: relative;
    overflow: hidden;
    background: #0a0e14;
}

.research-card-media img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
    transition: transform 0.5s ease;
}

.research-card-media:hover img {
    transform: scale(1.03);
}

/* Contain media — full-width, no crop */
.research-card-media.contain {
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--card-bg);
}

.research-card-media.contain img {
    width: 100%;
    height: auto;
    object-fit: contain;
}

/* Compact media — smaller image with padding */
.research-card-media.compact {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 1.5rem;
    background: var(--card-bg);
}

.research-card-media.compact img {
    width: 70%;
    height: auto;
    object-fit: contain;
    border-radius: 4px;
}

/* Dual image layout — two wide headers stacked vertically */
.research-card-media.dual {
    display: grid;
    grid-template-columns: 1fr;
    gap: 2px;
    padding: 0;
    background: #0a0e14;
}

.research-card-media.dual img {
    width: 100%;
    height: auto;
    object-fit: cover;
    display: block;
    transition: transform 0.5s ease;
}

.research-card-media.dual:hover img {
    transform: scale(1.03);
}

/* Triple image layout for multi-directional card */
.research-card-media.triple {
    display: grid;
    grid-template-columns: 1fr 1fr 1fr;
    gap: 2px;
    padding: 0;
}

.research-card-media.triple img {
    width: 100%;
    aspect-ratio: 1;
    object-fit: cover;
}

.research-card-body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    padding: 2rem 2.2rem;
}

.research-card-label {
    font-family: var(--font-mono);
    font-size: 0.68rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.14em;
    color: var(--card-label-color);
    background: var(--card-label-bg);
    display: inline-block;
    padding: 0.2rem 0.6rem;
    border-radius: 3px;
    margin-bottom: 0.6rem;
    width: fit-content;
}

.research-card-number {
    font-family: var(--font-mono);
    font-size: 0.65rem;
    font-weight: 500;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--text-tertiary);
    margin-bottom: 0.5rem;
}

.research-card-title {
    font-family: var(--font-display);
    font-size: 1.45rem;
    font-weight: 400;
    color: var(--card-text);
    line-height: 1.3;
    margin-bottom: 0.8rem;
}

.research-card-text {
    font-size: 0.92rem;
    line-height: 1.75;
    color: var(--card-text-secondary);
    margin-bottom: 1.2rem;
}

.research-card-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 0.6rem;
    align-items: center;
    margin-top: auto;
}

.card-link {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--card-label-color);
    padding: 0.35rem 0.85rem;
    border: 1px solid var(--card-border);
    border-radius: 5px;
    transition: all 0.25s;
}

.card-link:hover {
    background: var(--card-label-bg);
    border-color: var(--card-label-color);
    color: var(--card-label-color);
}

.card-link i {
    font-size: 0.75rem;
}

.card-citation {
    font-size: 0.78rem;
    color: var(--text-tertiary);
    font-style: italic;
}

/* ═══════════════════════════════════════════
   TECHNICAL STACK
   ═══════════════════════════════════════════ */

.stack-grid {
    display: flex;
    flex-direction: column;
    gap: 1.2rem;
}

.stack-row {
    display: flex;
    align-items: baseline;
    gap: 1rem;
}

.stack-label {
    font-family: var(--font-mono);
    font-size: 0.72rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-tertiary);
    min-width: 110px;
    flex-shrink: 0;
}

.stack-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 0.4rem;
}

.stack-tag {
    font-size: 0.82rem;
    font-weight: 500;
    color: var(--tag-text);
    background: var(--tag-bg);
    padding: 0.3rem 0.7rem;
    border-radius: 3px;
    transition: background-color 0.2s, color 0.2s;
    white-space: nowrap;
}

.stack-tag:hover {
    background: var(--accent-light);
    color: var(--accent);
}

/* (featured project section removed — merged into research cards) */

/* ═══════════════════════════════════════════
   PUBLICATIONS
   ═══════════════════════════════════════════ */

.pub-list {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.pub-item {
    padding: 1.2rem 1.5rem;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 6px;
    transition: box-shadow 0.3s, border-color 0.3s;
}

.pub-item:hover {
    box-shadow: var(--shadow-md);
}

.pub-authors {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

.pub-authors strong {
    color: var(--text);
    font-weight: 600;
}

.pub-title-text {
    font-family: var(--font-display);
    font-size: 1.1rem;
    color: var(--text);
    line-height: 1.4;
    margin-bottom: 0.35rem;
}

.pub-venue {
    font-size: 0.85rem;
    color: var(--text-tertiary);
    font-style: italic;
}

.pub-venue a {
    font-style: normal;
    font-weight: 500;
}

/* ═══════════════════════════════════════════
   OPEN SOURCE PROJECTS
   ═══════════════════════════════════════════ */

.projects-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

.project-card {
    padding: 1.4rem 1.5rem;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 6px;
    transition: box-shadow 0.3s, border-color 0.3s, transform 0.3s;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.project-card-img {
    display: block;
    width: calc(100% + 3rem);
    margin: -1.4rem -1.5rem 1rem;
    height: auto;
    object-fit: cover;
    border-bottom: 1px solid var(--border);
}

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

.project-card-header {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    margin-bottom: 0.6rem;
}

.project-card-header i {
    color: var(--text-tertiary);
    font-size: 1.1rem;
}

.project-card-name {
    font-family: var(--font-mono);
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--accent);
}

.project-card-slogan {
    display: block;
    font-size: 0.78rem;
    color: var(--accent);
    opacity: 0.75;
    margin-bottom: 0.6rem;
    letter-spacing: 0.01em;
}

.project-card-desc {
    font-size: 0.88rem;
    line-height: 1.6;
    color: var(--text-secondary);
    flex: 1;
}

.project-card-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 0.35rem;
    margin-top: 0.8rem;
}

.project-card.featured {
    border-color: var(--accent);
}

.project-badge {
    font-family: var(--font-mono);
    font-size: 0.62rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--accent);
    background: var(--accent-light);
    padding: 0.15rem 0.45rem;
    border-radius: 3px;
    margin-left: auto;
}

.project-card-tags span {
    font-size: 0.72rem;
    font-weight: 500;
    color: var(--text-tertiary);
    background: var(--tag-bg);
    padding: 0.15rem 0.5rem;
    border-radius: 3px;
}

/* ═══════════════════════════════════════════
   FOOTER
   ═══════════════════════════════════════════ */

.footer {
    text-align: center;
    padding: 2.5rem 2rem;
    border-top: 1px solid var(--border-light);
    background: var(--bg);
}

.footer p {
    font-size: 0.82rem;
    color: var(--text-tertiary);
    line-height: 1.6;
}

/* ═══════════════════════════════════════════
   THEME TOGGLE
   ═══════════════════════════════════════════ */

.theme-switch-wrapper {
    position: fixed;
    top: 1.2rem;
    right: 1.2rem;
    z-index: 3000;
}

.theme-switch {
    position: relative;
    display: inline-block;
    width: 52px;
    height: 28px;
    cursor: pointer;
}

.theme-switch input {
    opacity: 0;
    width: 0;
    height: 0;
    position: absolute;
}

.slider {
    position: absolute;
    inset: 0;
    background-color: rgba(255, 255, 255, 0.2);
    border-radius: 28px;
    transition: 0.35s;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 7px;
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border: 1px solid rgba(255, 255, 255, 0.15);
}

.slider::before {
    content: "";
    position: absolute;
    height: 20px;
    width: 20px;
    left: 4px;
    bottom: 3px;
    background-color: white;
    border-radius: 50%;
    transition: 0.35s;
    z-index: 2;
    box-shadow: 0 1px 4px rgba(0, 0, 0, 0.15);
}

.slider-icon {
    font-size: 11px;
    z-index: 1;
    transition: opacity 0.35s;
}

.slider-icon.light {
    color: #fbbf24;
    opacity: 1;
}

.slider-icon.dark {
    color: #fff;
    opacity: 0.6;
}

input:checked + .slider {
    background-color: rgba(255, 255, 255, 0.1);
}

input:checked + .slider::before {
    transform: translateX(24px);
}

input:checked + .slider .slider-icon.light {
    opacity: 0.3;
}

input:checked + .slider .slider-icon.dark {
    opacity: 1;
}

.theme-switch:hover .slider::before {
    box-shadow: 0 0 8px rgba(255, 255, 255, 0.3);
}

/* scrolled state — solid background */
.theme-switch-wrapper.scrolled .slider {
    background-color: var(--tag-bg);
    border-color: var(--border);
    backdrop-filter: none;
}

.theme-switch-wrapper.scrolled .slider-icon.light {
    color: #f59e0b;
}

.theme-switch-wrapper.scrolled .slider-icon.dark {
    color: var(--text-tertiary);
}

/* ═══════════════════════════════════════════
   SCROLL ANIMATIONS
   ═══════════════════════════════════════════ */

.fade-in {
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.5s ease, transform 0.5s ease;
}

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

/* staggered children */
.stagger-children > * {
    opacity: 0;
    transform: translateY(16px);
    transition: opacity 0.4s ease, transform 0.4s ease;
}

.stagger-children.visible > *:nth-child(1) { transition-delay: 0s; }
.stagger-children.visible > *:nth-child(2) { transition-delay: 0.06s; }
.stagger-children.visible > *:nth-child(3) { transition-delay: 0.12s; }
.stagger-children.visible > *:nth-child(4) { transition-delay: 0.18s; }
.stagger-children.visible > *:nth-child(5) { transition-delay: 0.24s; }

.stagger-children.visible > * {
    opacity: 1;
    transform: translateY(0);
}

/* ═══════════════════════════════════════════
   RESPONSIVE
   ═══════════════════════════════════════════ */

@media (max-width: 768px) {
    :root {
        --section-gap: 3.5rem;
    }

    #animation-container {
        height: 60vh;
        min-height: 400px;
    }

    .hero-overlay {
        padding: 2rem 1.5rem;
    }

    .hero-name {
        font-size: 2.2rem;
    }

    .hero-tagline {
        font-size: 0.95rem;
    }

    .page-content {
        padding: 0 1.25rem;
    }

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

    /* Cards stack vertically */
    .research-card {
        grid-template-columns: 1fr;
        margin-bottom: 2rem;
    }

    .research-card:nth-child(even) {
        direction: ltr;
    }

    .research-card-body {
        padding: 1.5rem;
    }

    .research-card-title {
        font-size: 1.25rem;
    }

    /* Stack rows */
    .stack-row {
        flex-direction: column;
        gap: 0.4rem;
    }

    .stack-label {
        min-width: unset;
    }

    /* Projects single column */
    .projects-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .hero-name {
        font-size: 1.8rem;
    }

    .hero-links {
        gap: 0.5rem;
    }

    .hero-links a {
        font-size: 0.82rem;
        padding: 0.3rem 0.5rem;
    }

    .research-card-media.triple {
        grid-template-columns: 1fr 1fr 1fr;
    }
}