/* ==========================================================================
   Hongyu He — personal site
   --------------------------------------------------------------------------
   Design notes, so future edits stay coherent:

   1. ONE accent colour (deep teal). No gradients anywhere.
   2. Type carries the hierarchy: serif display + system sans body.
      Size, weight and letter-spacing do the work that coloured boxes used to.
   3. Structure comes from whitespace and hairline rules — never nested cards.
   4. Zero external requests: system font stacks, inline SVG icons, no CDN.
      (Matters because Google Fonts is unreachable from parts of Asia.)
   5. Light and dark are both first-class; every colour is a token below.
   ========================================================================== */

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

:root {
    --paper:        #fbfaf8;
    --surface:      #f2f0eb;
    --ink:          #1c1b19;
    --ink-2:        #4a4844;
    --ink-3:        #7d7a72;
    --rule:         #e4e1d9;
    --accent:       #14615c;
    --accent-ink:   #0f4b47;
    --accent-soft:  #e7efee;
    --shadow:       0 1px 2px rgba(28, 27, 25, .05);

    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue",
                 Helvetica, Arial, "PingFang SC", "Hiragino Sans GB",
                 "Microsoft YaHei", sans-serif;
    --font-serif: "Iowan Old Style", "Palatino Linotype", Palatino,
                  "Book Antiqua", Georgia, "Times New Roman", "Songti SC", serif;
    --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;

    --measure: 66ch;
    --gutter: clamp(1.25rem, 5vw, 2.5rem);
}

@media (prefers-color-scheme: dark) {
    :root {
        --paper:        #131311;
        --surface:      #1c1b18;
        --ink:          #eae7e0;
        --ink-2:        #aaa69d;
        --ink-3:        #7f7c74;
        --rule:         #2c2a26;
        --accent:       #6fc0b8;
        --accent-ink:   #8ed3cb;
        --accent-soft:  #16302e;
        --shadow:       0 1px 2px rgba(0, 0, 0, .3);
    }
}

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

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

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

@media (prefers-reduced-motion: reduce) {
    html { scroll-behavior: auto; }
    *, *::before, *::after { animation-duration: .01ms !important; transition-duration: .01ms !important; }
}

body {
    margin: 0;
    background: var(--paper);
    color: var(--ink);
    font-family: var(--font-sans);
    font-size: 17px;
    line-height: 1.65;
    -webkit-font-smoothing: antialiased;
    text-rendering: optimizeLegibility;
}

h1, h2, h3, h4 { font-weight: 600; line-height: 1.25; margin: 0; }
p { margin: 0 0 1.1em; }
p:last-child { margin-bottom: 0; }

a {
    color: var(--accent);
    text-decoration: none;
    border-bottom: 1px solid color-mix(in srgb, var(--accent) 35%, transparent);
    transition: border-color .15s ease, color .15s ease;
}
a:hover { color: var(--accent-ink); border-bottom-color: var(--accent); }

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

img { max-width: 100%; height: auto; display: block; }

/* Skip link — keyboard users land on content, not the nav, every page. */
.skip {
    position: absolute;
    left: -9999px;
    top: 0;
    background: var(--accent);
    color: var(--paper);
    padding: .6rem 1rem;
    border: 0;
    z-index: 200;
}
.skip:focus { left: 0; }

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

.wrap {
    width: 100%;
    max-width: 62rem;
    margin-inline: auto;
    padding-inline: var(--gutter);
}

.prose { max-width: var(--measure); }

/* --- Site header / nav ---------------------------------------------------- */

.site-head {
    border-bottom: 1px solid var(--rule);
    background: color-mix(in srgb, var(--paper) 94%, transparent);
    backdrop-filter: saturate(180%) blur(12px);
    position: sticky;
    top: 0;
    z-index: 100;
}

.site-head .wrap {
    display: flex;
    align-items: baseline;
    justify-content: space-between;
    gap: 1.5rem;
    padding-block: 1rem;
    flex-wrap: wrap;
}

.wordmark {
    font-family: var(--font-serif);
    font-size: 1.0625rem;
    font-weight: 600;
    letter-spacing: .01em;
    color: var(--ink);
    border-bottom: 0;
    white-space: nowrap;
}
.wordmark:hover { color: var(--accent); }

.site-nav {
    display: flex;
    gap: clamp(1rem, 3vw, 1.9rem);
    align-items: baseline;
    flex-wrap: wrap;
}

.site-nav a {
    color: var(--ink-2);
    font-size: .9375rem;
    border-bottom: 1px solid transparent;
    padding-bottom: 2px;
}
.site-nav a:hover { color: var(--ink); border-bottom-color: var(--rule); }

.site-nav a[aria-current="page"] {
    color: var(--ink);
    font-weight: 500;
    border-bottom-color: var(--accent);
}

/* --- Page header ---------------------------------------------------------- */

/* No bottom margin: the following .section supplies its own top padding, and
   stacking both leaves a gap wide enough to read as a missing element. */
.page-head {
    padding-block: clamp(3rem, 8vw, 5rem) clamp(1.75rem, 4vw, 2.5rem);
    border-bottom: 1px solid var(--rule);
}

.page-title {
    font-family: var(--font-serif);
    font-size: clamp(2.1rem, 5.5vw, 2.9rem);
    font-weight: 600;
    letter-spacing: -.015em;
}

.page-standfirst {
    margin-top: .75rem;
    max-width: var(--measure);
    color: var(--ink-2);
    font-size: 1.0625rem;
}

/* --- Eyebrow label -------------------------------------------------------- */

.eyebrow {
    font-size: .72rem;
    font-weight: 600;
    letter-spacing: .12em;
    text-transform: uppercase;
    color: var(--ink-3);
    margin-bottom: 1.25rem;
}

/* --- Home hero ------------------------------------------------------------ */

.hero {
    display: grid;
    grid-template-columns: 168px 1fr;
    gap: clamp(1.75rem, 5vw, 3rem);
    align-items: start;
    padding-block: clamp(3rem, 8vw, 5rem) clamp(2.5rem, 6vw, 3.5rem);
    border-bottom: 1px solid var(--rule);
}

.hero-photo {
    width: 168px;
    height: 168px;
    object-fit: cover;
    border-radius: 3px;
    border: 1px solid var(--rule);
    box-shadow: var(--shadow);
    filter: saturate(.92);
}

.hero-name {
    font-family: var(--font-serif);
    font-size: clamp(2.3rem, 6vw, 3.1rem);
    font-weight: 600;
    letter-spacing: -.02em;
    line-height: 1.1;
}

.hero-role {
    margin-top: .6rem;
    font-size: 1.0625rem;
    color: var(--ink-2);
}

.hero-role strong { color: var(--ink); font-weight: 600; }

/* Research descriptor: subordinate to the affiliation line above it, so the two
   don't compete. Smaller, lighter, slightly tracked out. */
.hero-tagline {
    margin-top: .5rem;
    font-size: .9375rem;
    color: var(--ink-3);
    letter-spacing: .01em;
}

.hero-links {
    display: flex;
    flex-wrap: wrap;
    gap: .5rem;
    margin-top: 1.4rem;
    padding: 0;
    list-style: none;
}

.hero-links a {
    display: inline-flex;
    align-items: center;
    gap: .4rem;
    font-size: .875rem;
    color: var(--ink-2);
    background: var(--surface);
    border: 1px solid var(--rule);
    border-radius: 999px;
    padding: .32rem .85rem;
}
.hero-links a:hover {
    color: var(--accent);
    border-color: color-mix(in srgb, var(--accent) 45%, var(--rule));
    background: var(--accent-soft);
}
.hero-links svg { width: 14px; height: 14px; flex: none; }

/* --- Generic content section ---------------------------------------------- */

.section {
    padding-block: clamp(2.5rem, 6vw, 3.5rem);
    border-bottom: 1px solid var(--rule);
}
.section:last-of-type { border-bottom: 0; }

.section-title {
    font-family: var(--font-serif);
    font-size: 1.5rem;
    font-weight: 600;
    letter-spacing: -.01em;
    margin-bottom: 1.4rem;
}

/* --- Numbered research statements ----------------------------------------- */

.threads {
    list-style: none;
    margin: 0;
    padding: 0;
    counter-reset: thread;
    display: grid;
    gap: 1.6rem;
}

.threads > li {
    counter-increment: thread;
    display: grid;
    grid-template-columns: 2.2rem 1fr;
    gap: 1rem;
    max-width: calc(var(--measure) + 3.2rem);
}

.threads > li::before {
    content: counter(thread, decimal-leading-zero);
    font-family: var(--font-mono);
    font-size: .8125rem;
    color: var(--accent);
    padding-top: .3em;
    font-variant-numeric: tabular-nums;
}

.threads h3 {
    font-size: 1.0625rem;
    font-weight: 600;
    margin-bottom: .3rem;
}

.threads p { color: var(--ink-2); font-size: 1rem; }

/* --- Publication list ----------------------------------------------------- */

.pub-year {
    display: flex;
    align-items: center;
    gap: 1rem;
    font-family: var(--font-mono);
    font-size: .8125rem;
    letter-spacing: .06em;
    color: var(--ink-3);
    margin: 2.5rem 0 1.25rem;
}
.pub-year::after {
    content: "";
    flex: 1;
    height: 1px;
    background: var(--rule);
}
.pub-year:first-of-type { margin-top: 0; }

.pubs { list-style: none; margin: 0; padding: 0; display: grid; gap: 1.75rem; }

.pub { max-width: var(--measure); }

.pub-title {
    font-size: 1.0625rem;
    font-weight: 600;
    line-height: 1.4;
    margin-bottom: .35rem;
}

.pub-authors {
    font-size: .9375rem;
    color: var(--ink-2);
    margin-bottom: .2rem;
}
.pub-authors .me { color: var(--ink); font-weight: 600; }

.pub-venue {
    font-size: .9375rem;
    color: var(--ink-3);
    font-style: italic;
}

.pub-links {
    display: flex;
    flex-wrap: wrap;
    gap: .45rem;
    margin-top: .6rem;
}

.pub-links a {
    font-family: var(--font-mono);
    font-size: .75rem;
    letter-spacing: .03em;
    text-transform: uppercase;
    color: var(--ink-2);
    border: 1px solid var(--rule);
    border-radius: 3px;
    padding: .15rem .5rem;
    background: var(--surface);
}
.pub-links a:hover {
    color: var(--accent);
    border-color: color-mix(in srgb, var(--accent) 45%, var(--rule));
    background: var(--accent-soft);
}

/* --- CV entries ----------------------------------------------------------- */

.entries { display: grid; gap: 2.25rem; }

.entry {
    display: grid;
    grid-template-columns: 11rem 1fr;
    gap: 1.5rem;
    align-items: start;
}

.entry-period {
    font-family: var(--font-mono);
    font-size: .8125rem;
    color: var(--ink-3);
    padding-top: .28em;
    font-variant-numeric: tabular-nums;
}

.entry-body { max-width: var(--measure); }

.entry-title { font-size: 1.0625rem; font-weight: 600; }

.entry-org {
    font-size: .9375rem;
    color: var(--accent);
    margin-top: .1rem;
}

.entry-note {
    margin-top: .55rem;
    font-size: 1rem;
    color: var(--ink-2);
}

.entry-note strong { color: var(--ink); font-weight: 600; }

.entry-note ul { margin: .5rem 0 0; padding-left: 1.1rem; }
.entry-note li { margin-bottom: .3rem; }

/* --- Contact rows --------------------------------------------------------- */

.contact-list {
    list-style: none;
    margin: 0;
    padding: 0;
    display: grid;
    gap: .8rem;
    max-width: var(--measure);
}

.contact-list li {
    display: grid;
    grid-template-columns: 7rem 1fr;
    gap: 1rem;
    align-items: baseline;
    font-size: 1rem;
}

.contact-list dt, .contact-key {
    font-size: .72rem;
    font-weight: 600;
    letter-spacing: .12em;
    text-transform: uppercase;
    color: var(--ink-3);
}

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

.site-foot {
    border-top: 1px solid var(--rule);
    margin-top: clamp(3rem, 8vw, 5rem);
    padding-block: 2.5rem 3rem;
    color: var(--ink-3);
    font-size: .875rem;
}

.site-foot .wrap {
    display: flex;
    justify-content: space-between;
    gap: 1.5rem;
    flex-wrap: wrap;
}

.site-foot a { color: var(--ink-2); border-bottom-color: var(--rule); }
.site-foot a:hover { color: var(--accent); }

.foot-links { display: flex; gap: 1.25rem; flex-wrap: wrap; }

/* --- Responsive ----------------------------------------------------------- */

@media (max-width: 40rem) {
    body { font-size: 16px; }

    .hero {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }

    .hero-photo { width: 120px; height: 120px; }

    .entry { grid-template-columns: 1fr; gap: .35rem; }
    .entry-period { padding-top: 0; order: -1; }

    .threads > li { grid-template-columns: 1.8rem 1fr; gap: .75rem; }

    .contact-list li { grid-template-columns: 1fr; gap: .1rem; }

    .site-head .wrap { padding-block: .85rem; gap: .6rem; }
    .site-nav { gap: 1.1rem; }
}

/* --- Print ---------------------------------------------------------------- */

@media print {
    .site-head, .site-foot, .hero-links, .skip { display: none; }
    body { background: #fff; color: #000; font-size: 11pt; }
    a { color: #000; border: 0; }
    .entry, .pub, .prose { max-width: none; }
}