/* ============================================================
   Yifei Zhang — Personal Homepage
   Design: minimal academic / editorial ledger
   Shared by index.html and publications.html
   ============================================================ */

/* ---------- Design tokens ---------- */
:root {
    --bg: #fbfaf6;
    --bg-elev: #ffffff;
    --ink: #1d1b16;
    --ink-soft: #45413a;
    --muted: #837c6d;
    --line: #e4ded0;
    --accent: #2e4bd7;
    --accent-soft: rgba(46, 75, 215, 0.07);
    --gold: #a87c1f;

    --serif: "Fraunces", "Songti SC", "STSong", "Noto Serif CJK SC", serif;
    --text: "Newsreader", "Songti SC", "STSong", Georgia, serif;
    --mono: "IBM Plex Mono", "SF Mono", Menlo, Consolas, monospace;

    --content-w: 720px;
    --topbar-h: 64px;
}

[data-theme="dark"] {
    --bg: #171512;
    --bg-elev: #1f1c17;
    --ink: #eae6dc;
    --ink-soft: #c8c2b4;
    --muted: #96907f;
    --line: #36322a;
    --accent: #95a7f2;
    --accent-soft: rgba(149, 167, 242, 0.1);
    --gold: #cfa04a;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--text);
    font-size: 18px;
    line-height: 1.75;
    color: var(--ink);
    background-color: var(--bg);
    -webkit-font-smoothing: antialiased;
    text-rendering: optimizeLegibility;
    transition: background-color 0.25s ease, color 0.25s ease;
}

::selection {
    background: var(--accent);
    color: var(--bg);
}

a {
    color: var(--accent);
    text-decoration: none;
    text-underline-offset: 3px;
    transition: color 0.15s ease;
}

a:hover {
    text-decoration: underline;
}

img {
    max-width: 100%;
}

button {
    font-family: inherit;
    cursor: pointer;
}

.container {
    max-width: var(--content-w);
    margin: 0 auto;
    padding: 0 28px;
}

/* Custom scrollbar */
::-webkit-scrollbar {
    width: 10px;
}

::-webkit-scrollbar-track {
    background: var(--bg);
}

::-webkit-scrollbar-thumb {
    background: var(--line);
    border-radius: 5px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--muted);
}

/* ---------- Top bar ---------- */
.topbar {
    position: sticky;
    top: 0;
    z-index: 100;
    background: color-mix(in srgb, var(--bg) 82%, transparent);
    -webkit-backdrop-filter: blur(12px);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--line);
}

.topbar-inner {
    max-width: var(--content-w);
    margin: 0 auto;
    padding: 0 28px;
    height: var(--topbar-h);
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
}

.site-name {
    font-family: var(--serif);
    font-size: 1.1rem;
    font-weight: 500;
    color: var(--ink);
    letter-spacing: 0.01em;
    white-space: nowrap;
}

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

.topbar nav ul {
    list-style: none;
    display: flex;
    align-items: center;
    gap: 26px;
}

.topbar nav a {
    font-family: var(--mono);
    font-size: 0.8rem;
    font-weight: 500;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    color: var(--ink-soft);
    padding-bottom: 2px;
    border-bottom: 1px solid transparent;
}

.topbar nav a:hover {
    color: var(--accent);
    text-decoration: none;
}

.topbar nav a.active {
    color: var(--accent);
    border-bottom-color: var(--accent);
}

.theme-toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    background: none;
    border: 1px solid var(--line);
    border-radius: 50%;
    color: var(--ink-soft);
    font-size: 0.8rem;
    transition: border-color 0.15s ease, color 0.15s ease;
}

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

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

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

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

/* ---------- Hero ---------- */
.hero {
    display: flex;
    align-items: center;
    gap: 32px;
    padding: 56px 0 40px;
}

.hero-photo {
    width: 132px;
    height: 132px;
    border-radius: 50%;
    object-fit: cover;
    flex-shrink: 0;
    border: 1px solid var(--line);
    padding: 4px;
    background: var(--bg-elev);
}

.hero-text h1 {
    font-family: var(--serif);
    font-size: 2.5rem;
    font-weight: 500;
    line-height: 1.15;
    letter-spacing: -0.01em;
    color: var(--ink);
    margin-bottom: 6px;
}

.hero-sub {
    font-family: var(--serif);
    font-style: italic;
    font-size: 1.12rem;
    color: var(--muted);
    margin-bottom: 14px;
}

.hero-email {
    font-family: var(--mono);
    font-size: 0.88rem;
    margin-bottom: 14px;
    color: var(--ink-soft);
}

.hero-email i {
    color: var(--accent);
    margin-right: 6px;
    font-size: 0.82rem;
}

.social-links {
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
}

.social-links a {
    font-family: var(--mono);
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--ink-soft);
    letter-spacing: 0.02em;
}

.social-links a i {
    margin-right: 5px;
    color: var(--accent);
}

.social-links a:hover {
    color: var(--accent);
    text-decoration: none;
}

/* ---------- Sections ---------- */
main {
    padding-bottom: 60px;
}

section {
    margin-bottom: 56px;
    scroll-margin-top: calc(var(--topbar-h) + 24px);
}

.sec-head {
    display: flex;
    align-items: baseline;
    gap: 14px;
    border-bottom: 1px solid var(--line);
    padding-bottom: 10px;
    margin-bottom: 26px;
}

.sec-index {
    font-family: var(--mono);
    font-size: 0.82rem;
    font-weight: 500;
    color: var(--accent);
    letter-spacing: 0.05em;
}

.sec-head h2 {
    font-family: var(--serif);
    font-size: 1.55rem;
    font-weight: 500;
    letter-spacing: -0.01em;
    color: var(--ink);
}

.sec-note {
    margin-left: auto;
    font-family: var(--mono);
    font-size: 0.78rem;
    color: var(--muted);
}

.sec-note a {
    color: var(--muted);
    margin-left: 10px;
}

.sec-note a:hover {
    color: var(--accent);
    text-decoration: none;
}

/* ---------- About ---------- */
.about-text p {
    margin-bottom: 16px;
    color: var(--ink-soft);
    font-size: 1.07rem;
}

.about-text strong {
    color: var(--ink);
    font-weight: 600;
}

.about-text em {
    color: var(--accent);
    font-style: normal;
    font-weight: 600;
}

.job-callout {
    margin-top: 24px;
    padding: 16px 20px;
    border: 1px solid var(--line);
    border-left: 3px solid var(--accent);
    border-radius: 6px;
    background: var(--bg-elev);
    font-size: 0.98rem;
    color: var(--ink-soft);
}

.job-callout strong {
    color: var(--ink);
    font-weight: 600;
}

.resume-links {
    margin-top: 24px;
    padding: 16px 20px;
    border: 1px solid var(--line);
    border-radius: 6px;
    background: var(--bg-elev);
    font-family: var(--mono);
    font-size: 0.88rem;
    color: var(--ink-soft);
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 6px 14px;
}

.resume-links strong {
    color: var(--ink);
    font-weight: 500;
}

.resume-links a {
    font-weight: 500;
}

/* ---------- News ---------- */
.news-list {
    list-style: none;
}

.news-item {
    display: none;
    position: relative;
    padding: 9px 0;
    color: var(--ink-soft);
    border-bottom: 1px dashed var(--line);
}

.news-item:last-child {
    border-bottom: none;
}

.news-item.active {
    display: block;
}

.news-date {
    font-family: var(--mono);
    font-size: 0.84rem;
    font-weight: 500;
    color: var(--accent);
    margin-right: 10px;
    white-space: nowrap;
}

.news-item strong {
    color: var(--ink);
    font-weight: 600;
}

.news-item em {
    color: var(--accent);
    font-style: normal;
    font-weight: 600;
}

.pagination {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 22px;
    margin-top: 22px;
    font-family: var(--mono);
    font-size: 0.84rem;
}

.pagination-btn {
    background: none;
    border: none;
    color: var(--accent);
    font-family: var(--mono);
    font-size: 0.84rem;
    font-weight: 500;
    letter-spacing: 0.03em;
    padding: 4px 2px;
    border-bottom: 1px solid transparent;
    transition: border-color 0.15s ease;
}

.pagination-btn:hover:not(:disabled) {
    border-bottom-color: var(--accent);
}

.pagination-btn:disabled {
    color: var(--muted);
    opacity: 0.5;
    cursor: default;
}

.pagination-info {
    color: var(--muted);
    letter-spacing: 0.05em;
}

/* ---------- Publications (index) ---------- */
.pub-group {
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--bg-elev);
    padding: 26px 28px 10px;
    margin-bottom: 18px;
}

.pub-group-head {
    margin-bottom: 18px;
}

.pub-group-title {
    font-family: var(--serif);
    font-size: 1.35rem;
    font-weight: 500;
    color: var(--ink);
    margin-bottom: 8px;
}

.pub-group-summary {
    font-size: 0.98rem;
    color: var(--ink-soft);
    line-height: 1.7;
    margin-bottom: 12px;
}

.pub-group-actions a {
    font-family: var(--mono);
    font-size: 0.83rem;
    font-weight: 500;
}

.pub-entry {
    position: relative;
    padding: 18px 0;
    border-top: 1px solid var(--line);
}

.pub-group .pub-entry:first-of-type {
    border-top: 1px solid var(--line);
}

.pub-box {
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--bg-elev);
    padding: 22px 26px;
    margin-bottom: 18px;
}

.pub-title {
    font-family: var(--serif);
    font-size: 1.14rem;
    font-weight: 500;
    line-height: 1.45;
    color: var(--ink);
    margin-bottom: 6px;
}

.pub-title a {
    color: inherit;
}

.pub-title a:hover {
    color: var(--accent);
    text-decoration: none;
}

.pub-scene {
    font-family: var(--mono);
    font-size: 0.78rem;
    font-weight: 400;
    color: var(--muted);
    letter-spacing: 0.02em;
}

.pub-authors {
    font-size: 0.96rem;
    color: var(--muted);
    margin-bottom: 6px;
    line-height: 1.6;
}

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

.pub-meta {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 6px 16px;
    margin-bottom: 8px;
}

.pub-venue {
    display: inline-block;
    font-family: var(--mono);
    font-size: 0.78rem;
    font-weight: 500;
    letter-spacing: 0.07em;
    text-transform: uppercase;
    color: var(--accent);
    background: color-mix(in srgb, var(--accent) 16%, transparent);
    padding: 2px 8px;
    border-radius: 3px;
}

.pub-venue.preprint {
    background: none;
    color: var(--muted);
    padding: 2px 0;
}

.pub-award {
    font-family: var(--mono);
    font-size: 0.78rem;
    font-weight: 500;
    letter-spacing: 0.03em;
    color: var(--gold);
}

.pub-award a {
    color: inherit;
}

.pub-desc,
.pub-tldr {
    font-size: 0.98rem;
    color: var(--ink-soft);
    line-height: 1.7;
    margin-bottom: 10px;
}

.pub-tldr strong {
    color: var(--ink);
    font-weight: 600;
}

.pub-tldr > strong:first-child {
    font-family: var(--mono);
    font-size: 0.78rem;
    font-weight: 500;
    letter-spacing: 0.05em;
    color: var(--muted);
    text-transform: uppercase;
    margin-right: 4px;
}

.pub-links {
    display: flex;
    flex-wrap: wrap;
    gap: 8px 18px;
    align-items: center;
}

.pub-links a {
    font-family: var(--mono);
    font-size: 0.8rem;
    font-weight: 500;
    letter-spacing: 0.03em;
    display: inline-flex;
    align-items: center;
    gap: 5px;
}

.pub-links a:hover {
    text-decoration: none;
    opacity: 0.75;
}

.github-stars {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    margin-left: 4px;
    padding: 1px 7px;
    border: 1px solid var(--line);
    border-radius: 999px;
    font-size: 0.72rem;
    color: var(--muted);
    font-weight: 400;
}

.github-stars i {
    color: var(--gold);
    font-size: 0.64rem;
}

/* ---------- Experiences ---------- */
.sec-head-gap {
    margin-top: 46px;
}

.exp-item {
    position: relative;
    display: grid;
    grid-template-columns: 40px 1fr;
    gap: 18px;
    padding: 16px 0;
    border-bottom: 1px dashed var(--line);
}

.exp-item:last-child {
    border-bottom: none;
}

.exp-logo-wrap {
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    border: 1px solid var(--line);
    border-radius: 6px;
    background: var(--bg-elev);
    overflow: hidden;
}

.exp-logo {
    width: 24px;
    height: 24px;
    object-fit: contain;
}

.exp-logo-icon {
    font-size: 1rem;
    color: var(--muted);
}

.logo-dark {
    display: none;
}

[data-theme="dark"] .logo-dark {
    display: block;
}

[data-theme="dark"] .logo-light {
    display: none;
}

.exp-header {
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    gap: 16px;
    flex-wrap: wrap;
}

.exp-title {
    font-family: var(--serif);
    font-size: 1.12rem;
    font-weight: 500;
    color: var(--ink);
}

.exp-date {
    font-family: var(--mono);
    font-size: 0.8rem;
    color: var(--muted);
    white-space: nowrap;
}

.exp-role {
    font-size: 0.98rem;
    color: var(--ink-soft);
    margin-top: 2px;
}

.exp-advisor {
    font-size: 0.93rem;
    color: var(--muted);
    margin-top: 2px;
}

/* ---------- Margin notes (Tufte-style dates, wide screens) ---------- */
@media (min-width: 1180px) {
    .news-item .news-date {
        position: absolute;
        right: calc(100% + 22px);
        top: 12px;
        margin-right: 0;
    }

    .exp-item .exp-date {
        position: absolute;
        right: calc(100% + 22px);
        top: 22px;
        text-align: right;
        width: 130px;
    }
}

/* ---------- Publications page ---------- */
.page-head {
    padding: 64px 0 10px;
}

.page-title {
    font-family: var(--serif);
    font-size: 2.6rem;
    font-weight: 500;
    letter-spacing: -0.01em;
    color: var(--ink);
    margin-bottom: 10px;
}

.page-subtitle {
    font-size: 0.98rem;
    color: var(--muted);
    margin-bottom: 4px;
}

.filter-tags {
    display: flex;
    gap: 26px;
    margin: 26px 0 12px;
    border-bottom: 1px solid var(--line);
    padding-bottom: 12px;
}

.filter-tag {
    font-family: var(--mono);
    font-size: 0.82rem;
    font-weight: 500;
    letter-spacing: 0.07em;
    text-transform: uppercase;
    color: var(--muted);
    cursor: pointer;
    padding-bottom: 3px;
    border-bottom: 2px solid transparent;
    transition: color 0.15s ease, border-color 0.15s ease;
    user-select: none;
}

.filter-tag:hover {
    color: var(--accent);
}

.filter-tag.active {
    color: var(--accent);
    border-bottom-color: var(--accent);
}

.year-section {
    margin-top: 34px;
}

.year-header {
    font-family: var(--serif);
    font-size: 1.9rem;
    font-weight: 500;
    color: var(--ink);
    border-bottom: 1px solid var(--line);
    padding-bottom: 8px;
    margin-bottom: 8px;
}

.publication-card {
    display: flex;
    gap: 26px;
    padding: 26px 0;
    border-bottom: 1px solid var(--line);
}

.publication-card.hidden {
    display: none;
}

.publication-card .pub-entry-body {
    flex: 1;
    min-width: 0;
}

.pub-thumb {
    flex-shrink: 0;
    width: 264px;
    height: 165px;
    border: 1px solid var(--line);
    border-radius: 6px;
    overflow: hidden;
    background: #ffffff;
    display: flex;
    align-items: center;
    justify-content: center;
    order: 2;
}

.pub-thumb img {
    max-width: 100%;
    max-height: 100%;
    object-fit: contain;
    display: block;
}

.abstract-box {
    display: none;
    margin-top: 12px;
    padding: 14px 18px;
    background: var(--accent-soft);
    border-left: 2px solid var(--accent);
    border-radius: 0 6px 6px 0;
    font-size: 0.92rem;
    line-height: 1.7;
    color: var(--ink-soft);
}

.abstract-box strong {
    color: var(--ink);
}

/* ---------- Footer ---------- */
footer {
    border-top: 1px solid var(--line);
    padding: 34px 0 44px;
    margin-top: 20px;
}

footer .container {
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    flex-wrap: wrap;
    gap: 6px 20px;
}

footer p {
    font-family: var(--mono);
    font-size: 0.78rem;
    color: var(--muted);
    letter-spacing: 0.02em;
}

footer a {
    color: var(--muted);
}

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

/* ---------- WeChat modal ---------- */
.wechat-modal {
    display: none;
    position: fixed;
    z-index: 9999;
    inset: 0;
    background: rgba(15, 13, 10, 0.6);
    -webkit-backdrop-filter: blur(4px);
    backdrop-filter: blur(4px);
}

.wechat-modal.active {
    display: flex;
    justify-content: center;
    align-items: center;
    animation: fadeIn 0.2s ease;
}

.wechat-content {
    background: var(--bg-elev);
    border: 1px solid var(--line);
    padding: 32px;
    border-radius: 10px;
    max-width: 380px;
    width: calc(100% - 48px);
    text-align: center;
    position: relative;
    animation: slideIn 0.25s ease;
}

.wechat-close {
    position: absolute;
    right: 16px;
    top: 10px;
    font-size: 26px;
    font-weight: 300;
    color: var(--muted);
    cursor: pointer;
    line-height: 1;
}

.wechat-close:hover {
    color: var(--ink);
}

.wechat-content h3 {
    font-family: var(--serif);
    font-weight: 500;
    margin-bottom: 18px;
    color: var(--ink);
    font-size: 1.15rem;
}

.wechat-content h3 i {
    color: #09bb07;
    margin-right: 6px;
}

.wechat-content img {
    max-width: 100%;
    border-radius: 6px;
    border: 1px solid var(--line);
}

.wechat-content p {
    margin-top: 14px;
    font-family: var(--mono);
    color: var(--muted);
    font-size: 0.78rem;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

@keyframes slideIn {
    from {
        transform: translateY(-16px);
        opacity: 0;
    }
    to {
        transform: translateY(0);
        opacity: 1;
    }
}

/* ---------- Back to top ---------- */
.back-to-top {
    position: fixed;
    bottom: 28px;
    right: 28px;
    width: 42px;
    height: 42px;
    background: var(--bg-elev);
    color: var(--ink-soft);
    border: 1px solid var(--line);
    border-radius: 50%;
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.25s ease, visibility 0.25s ease, color 0.15s ease, border-color 0.15s ease;
    z-index: 999;
    display: flex;
    align-items: center;
    justify-content: center;
}

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

.back-to-top:hover {
    color: var(--accent);
    border-color: var(--accent);
}

/* ---------- Reveal animations ---------- */
.js .reveal {
    opacity: 0;
    transform: translateY(14px);
}

.js .reveal.visible {
    opacity: 1;
    transform: none;
    transition: opacity 0.7s ease, transform 0.7s ease;
}

.js .hero > * {
    animation: riseIn 0.7s ease both;
}

.js .hero > *:nth-child(2) {
    animation-delay: 0.08s;
}

@keyframes riseIn {
    from {
        opacity: 0;
        transform: translateY(14px);
    }
    to {
        opacity: 1;
        transform: none;
    }
}

@media (prefers-reduced-motion: reduce) {
    html {
        scroll-behavior: auto;
    }

    .js .reveal,
    .js .reveal.visible,
    .js .hero > * {
        opacity: 1;
        transform: none;
        animation: none;
        transition: none;
    }
}

/* ---------- Responsive ---------- */
@media (max-width: 768px) {
    body {
        font-size: 16.5px;
    }

    .container {
        padding: 0 20px;
    }

    .topbar-inner {
        padding: 0 20px;
        height: auto;
        min-height: var(--topbar-h);
        flex-wrap: wrap;
        padding-top: 10px;
        padding-bottom: 10px;
    }

    .topbar nav ul {
        gap: 16px;
        flex-wrap: wrap;
    }

    .hero {
        flex-direction: column;
        text-align: center;
        gap: 22px;
        padding: 40px 0 30px;
    }

    .hero-text h1 {
        font-size: 1.95rem;
    }

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

    section {
        margin-bottom: 44px;
    }

    .pub-group {
        padding: 20px 20px 6px;
    }

    .publication-card {
        flex-direction: column;
        gap: 16px;
    }

    .pub-thumb {
        order: 0;
        width: 100%;
        height: 190px;
    }

    .page-title {
        font-size: 2rem;
    }

    footer .container {
        flex-direction: column;
        gap: 4px;
    }
}

@media (max-width: 480px) {
    .hero-text h1 {
        font-size: 1.7rem;
    }

    .exp-item {
        grid-template-columns: 34px 1fr;
        gap: 12px;
    }

    .exp-logo-wrap {
        width: 34px;
        height: 34px;
    }

    .exp-date {
        white-space: normal;
    }

    .pagination {
        gap: 14px;
    }
}

/* ---------- Print ---------- */
@media print {
    .topbar,
    .back-to-top,
    .pagination,
    .theme-toggle {
        display: none !important;
    }

    body {
        background: #fff;
        color: #000;
        font-size: 11pt;
    }

    .news-item {
        display: block !important;
    }

    section {
        page-break-inside: avoid;
    }
}