/* ============================================================
   Haoxian Yan — personal site
   Plain CSS, no build step, no external requests.

   Theming uses light-dark() with color-scheme, so the entire
   palette is declared once. Switching themes only changes
   `color-scheme` on :root — no duplicated token blocks, and
   with JS disabled the site still follows the OS preference.
   ============================================================ */

/* ---------- Reset ---------- */

*,
*::before,
*::after {
    box-sizing: border-box;
}

* {
    margin: 0;
}

html {
    -webkit-text-size-adjust: 100%;
    scroll-behavior: smooth;
}

img,
svg {
    display: block;
    max-width: 100%;
}

button {
    font: inherit;
    color: inherit;
    background: none;
    border: none;
    cursor: pointer;
}

/* ---------- Tokens ---------- */

:root {
    color-scheme: light dark;

    --bg:            light-dark(#fafaf9, #0c0a09);
    --surface:       light-dark(#ffffff, #1c1917);
    --surface-sunk:  light-dark(#f5f5f4, #141110);
    --border:        light-dark(#e7e5e4, #2c2724);
    --border-strong: light-dark(#d6d3d1, #3b3532);

    --text:    light-dark(#1c1917, #eae7e4);
    --muted:   light-dark(#57534e, #a8a29e);
    --faint:   light-dark(#78716c, #948d87);

    --accent:      light-dark(#0e7490, #22d3ee);
    --accent-soft: light-dark(#ecfeff, #0d3f4a);
    --accent-line: light-dark(#67e8f9, #155e6e);

    --font-serif: "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, "Times New Roman", serif;
    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;

    --radius: 12px;
    --radius-sm: 8px;
    --container: 62rem;
    --nav-h: 3.5rem;

    --shadow: 0 1px 2px light-dark(rgb(28 25 23 / 0.05), rgb(0 0 0 / 0.3)),
              0 4px 16px light-dark(rgb(28 25 23 / 0.04), rgb(0 0 0 / 0.24));
}

:root[data-theme="light"] { color-scheme: light; }
:root[data-theme="dark"]  { color-scheme: dark; }

/* ---------- Base ---------- */

body {
    background: var(--bg);
    color: var(--text);
    font-family: var(--font-sans);
    font-size: 1rem;
    line-height: 1.65;
    -webkit-font-smoothing: antialiased;
    text-rendering: optimizeLegibility;
}

h1, h2, h3, h4 {
    font-family: var(--font-serif);
    font-weight: 600;
    line-height: 1.2;
    letter-spacing: -0.01em;
    text-wrap: balance;
}

p, li {
    text-wrap: pretty;
}

a {
    color: var(--accent);
    text-decoration-thickness: 1px;
    text-underline-offset: 0.2em;
}

a:hover {
    text-decoration-thickness: 2px;
}

code {
    font-family: var(--font-mono);
    font-size: 0.875em;
    background: var(--surface-sunk);
    border: 1px solid var(--border);
    border-radius: 4px;
    padding: 0.1em 0.35em;
}

:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 3px;
    border-radius: 2px;
}

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

/* ---------- Layout ---------- */

.container {
    width: 100%;
    max-width: var(--container);
    margin-inline: auto;
    padding-inline: clamp(1.125rem, 5vw, 2rem);
}

.section {
    padding-block: clamp(3rem, 7vw, 5rem);
    scroll-margin-top: calc(var(--nav-h) + 1rem);
}

.section + .section {
    border-top: 1px solid var(--border);
}

.section-head {
    margin-bottom: 2.25rem;
}

.section-head h2 {
    font-size: clamp(1.6rem, 3.5vw, 2.1rem);
}

.section-head .lede {
    margin-top: 0.75rem;
    max-width: 60ch;
    color: var(--muted);
}

.eyebrow {
    display: block;
    margin-bottom: 0.6rem;
    font-family: var(--font-sans);
    font-size: 0.75rem;
    font-weight: 600;
    letter-spacing: 0.1em;
    text-transform: uppercase;
    color: var(--accent);
}

/* ---------- Skip link ---------- */

.skip {
    position: absolute;
    left: 0.75rem;
    top: -4rem;
    z-index: 100;
    background: var(--surface);
    color: var(--text);
    border: 1px solid var(--border-strong);
    border-radius: var(--radius-sm);
    padding: 0.6rem 1rem;
    text-decoration: none;
    transition: top 0.15s ease;
}

.skip:focus {
    top: 0.75rem;
}

/* ---------- Nav ---------- */

.nav {
    position: sticky;
    top: 0;
    z-index: 50;
    height: var(--nav-h);
    background: var(--bg);
    background: color-mix(in srgb, var(--bg) 82%, transparent);
    backdrop-filter: saturate(180%) blur(12px);
    -webkit-backdrop-filter: saturate(180%) blur(12px);
    border-bottom: 1px solid var(--border);
}

.nav .container {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    height: 100%;
}

.nav-brand {
    font-family: var(--font-serif);
    font-size: 1rem;
    font-weight: 600;
    color: var(--text);
    text-decoration: none;
    margin-right: auto;
    white-space: nowrap;
}

.nav-links {
    display: flex;
    align-items: center;
    gap: 0.15rem;
    list-style: none;
    padding: 0;
    overflow-x: auto;
    scrollbar-width: none;
}

.nav-links::-webkit-scrollbar {
    display: none;
}

.nav-links a {
    display: block;
    padding: 0.4rem 0.7rem;
    border-radius: var(--radius-sm);
    font-size: 0.9rem;
    color: var(--muted);
    text-decoration: none;
    white-space: nowrap;
    transition: color 0.15s ease, background-color 0.15s ease;
}

.nav-links a:hover {
    color: var(--text);
    background: var(--surface-sunk);
}

.nav-links a[aria-current="true"] {
    color: var(--accent);
    background: var(--accent-soft);
}

/* Theme toggle: swap which glyph is visible based on resolved scheme. */
.theme-toggle {
    display: grid;
    place-items: center;
    flex: none;
    width: 2.25rem;
    height: 2.25rem;
    margin-left: 0.35rem;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--muted);
    transition: color 0.15s ease, border-color 0.15s ease;
}

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

.theme-toggle svg {
    width: 1.05rem;
    height: 1.05rem;
    grid-area: 1 / 1;
    stroke: currentColor;
    fill: none;
    stroke-width: 1.7;
    stroke-linecap: round;
    stroke-linejoin: round;
}

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

@media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) .theme-toggle .icon-sun  { display: block; }
    :root:not([data-theme="light"]) .theme-toggle .icon-moon { display: none; }
}

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

/* ---------- Hero ---------- */

.hero {
    padding-block: clamp(3.5rem, 9vw, 6.5rem) clamp(3rem, 6vw, 4.5rem);
    border-bottom: 1px solid var(--border);
}

.hero h1 {
    font-size: clamp(2.4rem, 7vw, 4rem);
    letter-spacing: -0.025em;
}

.hero .container {
    display: flow-root;
}

.hero-portrait {
    float: right;
    width: clamp(10rem, 24vw, 16rem);
    height: auto;
    margin: 0 0 1.5rem 2rem;
    border-radius: var(--radius);
    border: 1px solid var(--border);
}

/* ---------- Photography ---------- */

.photo-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(min(100%, 15rem), 1fr));
    gap: 1.75rem 1.25rem;
}

.photo-grid figure {
    min-width: 0;
}

.photo-grid img,
.research-photo img,
.collaborator-photo img {
    width: 100%;
    height: auto;
    border: 1px solid var(--border);
    border-radius: var(--radius);
}

figcaption {
    margin-top: 0.65rem;
    font-size: 0.875rem;
    color: var(--muted);
}

.research-photo {
    max-width: 44rem;
    margin-top: 1.75rem;
}

.collaborator-photo {
    max-width: 26rem;
    margin-top: 1.25rem;
}

@media (max-width: 40rem) {
    .hero-portrait {
        float: none;
        width: 11rem;
        margin: 0 0 1.5rem;
    }
}

.hero-role {
    margin-top: 0.85rem;
    font-size: clamp(1.05rem, 2.2vw, 1.2rem);
    color: var(--muted);
    max-width: 46ch;
}

.hero-bio {
    margin-top: 1.5rem;
    max-width: 58ch;
}

.hero-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem 1.25rem;
    margin-top: 1.75rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border);
    font-size: 0.875rem;
    color: var(--faint);
}

.hero-meta > * {
    display: flex;
    align-items: center;
    gap: 0.45rem;
}

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.7rem;
    margin-top: 1.75rem;
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: 0.45rem;
    padding: 0.6rem 1.1rem;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-strong);
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--text);
    text-decoration: none;
    transition: border-color 0.15s ease, background-color 0.15s ease, transform 0.15s ease;
}

.btn:hover {
    background: var(--surface-sunk);
    border-color: var(--faint);
}

.btn:active {
    transform: translateY(1px);
}

.btn-primary {
    background: var(--accent);
    border-color: var(--accent);
    color: light-dark(#ffffff, #06181d);
}

.btn-primary:hover {
    background: color-mix(in srgb, var(--accent) 88%, var(--text));
    border-color: transparent;
}

/* ---------- Cards ---------- */

.card {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: clamp(1.35rem, 3.5vw, 2rem);
    box-shadow: var(--shadow);
}

.card + .card {
    margin-top: 1.25rem;
}

.card-head {
    display: flex;
    flex-wrap: wrap;
    align-items: baseline;
    gap: 0.5rem 1rem;
}

.card-head h3 {
    font-size: 1.4rem;
}

.card-sub {
    margin-top: 0.4rem;
    font-size: 0.875rem;
    color: var(--faint);
}

.card-lede {
    margin-top: 1rem;
    max-width: 70ch;
}

/* ---------- Paper ---------- */

.paper {
    border-left: 3px solid var(--accent);
    background: var(--surface);
    border-radius: 0 var(--radius) var(--radius) 0;
    padding: clamp(1.25rem, 3vw, 1.75rem);
    margin-block: 1.75rem;
}

.paper-title {
    font-size: 1.2rem;
    line-height: 1.35;
}

.paper-authors {
    margin-top: 0.6rem;
    color: var(--muted);
    font-size: 0.95rem;
}

.paper-authors .me {
    color: var(--text);
    font-weight: 600;
    border-bottom: 2px solid var(--accent-line);
}

.paper-note {
    margin-top: 0.9rem;
    font-size: 0.85rem;
    color: var(--faint);
}

/* ---------- Pills & tags ---------- */

.pills {
    display: flex;
    flex-wrap: wrap;
    gap: 0.4rem;
    margin-top: 0.9rem;
    list-style: none;
    padding: 0;
}

.pill {
    display: inline-block;
    max-width: 100%;
    padding: 0.2rem 0.6rem;
    border-radius: 999px;
    border: 1px solid var(--border-strong);
    background: var(--surface-sunk);
    font-size: 0.75rem;
    color: var(--muted);
    /* Deliberately not nowrap: a long venue name would otherwise
       force horizontal page scroll on narrow screens. */
}

.pill-accent {
    border-color: var(--accent-line);
    background: var(--accent-soft);
    color: var(--accent);
}

/* ---------- Link lists ---------- */

.linklist {
    list-style: none;
    padding: 0;
    margin-top: 1.25rem;
    border-top: 1px solid var(--border);
}

.linklist li {
    border-bottom: 1px solid var(--border);
}

.linklist a {
    display: flex;
    flex-wrap: wrap;
    align-items: baseline;
    gap: 0.25rem 0.75rem;
    padding: 0.75rem 0.25rem;
    text-decoration: none;
    color: var(--text);
    transition: padding-left 0.15s ease, color 0.15s ease;
}

.linklist a:hover {
    color: var(--accent);
    padding-left: 0.6rem;
}

.linklist a::after {
    content: "→";
    margin-left: auto;
    color: var(--faint);
    transition: transform 0.15s ease, color 0.15s ease;
}

.linklist a:hover::after {
    color: var(--accent);
    transform: translateX(3px);
}

.linklist .note {
    font-size: 0.85rem;
    color: var(--faint);
    font-weight: 400;
}

.linklist a > span:first-child {
    font-weight: 500;
}

/* ---------- Callout / disclosure ---------- */

.callout {
    margin-top: 1.75rem;
    padding: clamp(1.1rem, 3vw, 1.5rem);
    background: var(--accent-soft);
    border: 1px solid var(--accent-line);
    border-radius: var(--radius);
}

.callout h4 {
    font-size: 1.05rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.callout h4::before {
    content: "";
    width: 0.5rem;
    height: 0.5rem;
    border-radius: 50%;
    background: var(--accent);
    flex: none;
}

.callout p + p {
    margin-top: 0.85rem;
}

.callout > p:first-of-type {
    margin-top: 0.85rem;
}

/* ---------- Details / accordions ---------- */

.accordions {
    margin-top: 1.5rem;
    border-top: 1px solid var(--border);
}

details {
    border-bottom: 1px solid var(--border);
}

summary {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.85rem 0.25rem;
    cursor: pointer;
    font-size: 0.95rem;
    font-weight: 500;
    list-style: none;
    transition: color 0.15s ease;
}

summary::-webkit-details-marker {
    display: none;
}

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

summary::after {
    content: "";
    margin-left: auto;
    width: 0.5rem;
    height: 0.5rem;
    border-right: 1.5px solid currentColor;
    border-bottom: 1.5px solid currentColor;
    transform: rotate(45deg) translate(-2px, -2px);
    transition: transform 0.2s ease;
    color: var(--faint);
    flex: none;
}

details[open] > summary::after {
    transform: rotate(-135deg) translate(-2px, -2px);
}

details[open] > summary {
    color: var(--accent);
}

.details-body {
    padding: 0.25rem 0.25rem 1.4rem;
    max-width: 72ch;
}

.details-body > * + * {
    margin-top: 0.9rem;
}

.details-body p {
    color: var(--muted);
}

.details-body strong {
    color: var(--text);
}

.details-body ul {
    padding-left: 1.1rem;
    color: var(--muted);
}

.details-body li + li {
    margin-top: 0.5rem;
}

/* ---------- Apps ---------- */

.jumpbar {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-bottom: 2rem;
    list-style: none;
    padding: 0;
}

.jumpbar a {
    display: inline-block;
    padding: 0.35rem 0.8rem;
    border: 1px solid var(--border-strong);
    border-radius: 999px;
    font-size: 0.85rem;
    color: var(--muted);
    text-decoration: none;
    transition: all 0.15s ease;
}

.jumpbar a:hover {
    color: var(--accent);
    border-color: var(--accent);
    background: var(--accent-soft);
}

.app + .app {
    margin-top: 1.25rem;
}

.app {
    scroll-margin-top: calc(var(--nav-h) + 1rem);
}

.storeslot {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    margin-top: 1.5rem;
    padding: 0.55rem 0.95rem;
    border: 1px dashed var(--border-strong);
    border-radius: var(--radius-sm);
    font-size: 0.825rem;
    color: var(--faint);
}

.storeslot::before {
    content: "";
    width: 0.45rem;
    height: 0.45rem;
    border-radius: 50%;
    background: var(--faint);
    opacity: 0.6;
}

.privacy-link {
    display: inline-block;
    margin-top: 1.25rem;
    font-size: 0.9rem;
}

/* ---------- Next / plans grid ---------- */

.grid-2 {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(min(100%, 16rem), 1fr));
    gap: 1rem;
}

.mini {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.25rem;
}

.mini h3 {
    font-size: 1rem;
    font-family: var(--font-sans);
    font-weight: 600;
}

.mini p {
    margin-top: 0.5rem;
    font-size: 0.9rem;
    color: var(--muted);
}

/* ---------- Footer ---------- */

.footer {
    border-top: 1px solid var(--border);
    background: var(--surface-sunk);
    padding-block: clamp(2.5rem, 6vw, 4rem);
}

.footer-grid {
    display: flex;
    flex-wrap: wrap;
    gap: 2rem;
    justify-content: space-between;
    align-items: flex-start;
}

.footer h2 {
    font-size: 1.3rem;
}

.footer p {
    margin-top: 0.6rem;
    color: var(--muted);
    max-width: 44ch;
    font-size: 0.925rem;
}

.footer-links {
    list-style: none;
    padding: 0;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    font-size: 0.925rem;
}

.footer-base {
    margin-top: 2.5rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border);
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    justify-content: space-between;
    font-size: 0.825rem;
    color: var(--faint);
}

/* ---------- Prose (privacy policy) ---------- */

.prose {
    max-width: 68ch;
}

.prose h2 {
    font-size: 1.75rem;
}

.prose h3 {
    font-size: 1.15rem;
    margin-top: 2.25rem;
    padding-top: 0.25rem;
}

.prose p {
    margin-top: 0.9rem;
    color: var(--muted);
}

.prose strong {
    color: var(--text);
}

.prose .updated {
    margin-top: 0.5rem;
    font-size: 0.85rem;
    color: var(--faint);
}

.prose ul {
    margin-top: 0.9rem;
    padding-left: 1.15rem;
    color: var(--muted);
}

.prose li + li {
    margin-top: 0.6rem;
}

/* ---------- Motion & print ---------- */

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

    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

@media print {
    .nav,
    .skip,
    .theme-toggle,
    .jumpbar,
    .storeslot,
    .hero-actions {
        display: none !important;
    }

    body {
        background: #fff;
        color: #000;
    }

    .card,
    .paper,
    .callout {
        box-shadow: none;
        border: 1px solid #ccc;
        break-inside: avoid;
    }

    details {
        break-inside: avoid;
    }

    /* Expand every accordion so nothing is lost on paper. */
    .details-body {
        display: block !important;
    }

    a[href^="http"]::after {
        content: " (" attr(href) ")";
        font-size: 0.75em;
        color: #555;
        word-break: break-all;
    }
}