/* =========================================================================
   Kuan-Yu Chen (Daniel) — personal academic site
   Pure CSS · Light/Dark · Responsive · Reduced-motion friendly
   Restrained, editorial, professional.
   ========================================================================= */

:root {
  --font-serif: "Newsreader", Georgia, "Times New Roman", serif;
  --font-sans: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, monospace;

  --maxw: 1080px;
  --gutter: clamp(1.25rem, 4vw, 3rem);
  --radius: 14px;
  --radius-sm: 9px;
  --transition: 180ms ease;

  /* Light theme */
  --bg: #fbfbf9;
  --bg-elev: #ffffff;
  --bg-sunken: #f2f1ec;
  --text: #1a1a1a;
  --text-soft: #565654;
  --text-faint: #6d6d67;
  --border: #e6e4dd;
  --border-strong: #d2cfc6;
  --accent: #1f5c8c;      /* muted academic blue */
  --accent-soft: #2f7bb5;
  --accent-tint: rgba(31, 92, 140, 0.08);
  --on-accent: #ffffff;   /* text/icons on an accent-filled control */
  --shadow: 0 1px 2px rgba(20, 20, 20, 0.04), 0 10px 30px -18px rgba(20, 20, 20, 0.25);
  --header-h: 61px;
}

[data-theme="dark"] {
  --bg: #111214;
  --bg-elev: #191a1d;
  --bg-sunken: #0d0e10;
  --text: #ececea;
  --text-soft: #adadaa;
  --text-faint: #93938c;
  --border: #2a2b2e;
  --border-strong: #3a3b3f;
  --accent: #6fb2e0;
  --accent-soft: #8ec5ec;
  --accent-tint: rgba(111, 178, 224, 0.12);
  --on-accent: #0b1a24;   /* dark text on the light-blue dark-theme accent */
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 14px 40px -20px rgba(0, 0, 0, 0.6);
}

*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: .001ms !important; transition-duration: .001ms !important; }
}

body {
  margin: 0; 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;
}

a { color: var(--accent); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--accent-soft); }
h1, h2, h3, h4 { line-height: 1.2; margin: 0; font-weight: 600; }
p { margin: 0; }
img { max-width: 100%; display: block; }

.ic { width: 1em; height: 1em; display: inline-block; vertical-align: -0.125em; fill: currentColor; flex: none; }

.skip-link { position: absolute; left: -999px; top: 0; background: var(--accent); color: var(--on-accent); padding: .6rem 1rem; border-radius: 0 0 var(--radius-sm) 0; z-index: 1000; }
.skip-link:focus { left: 0; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-radius: 3px; }

/* ---- Header / Nav ---- */
.site-header {
  position: sticky; top: 0; z-index: 100;
  background: var(--bg);
  background: color-mix(in srgb, var(--bg) 90%, transparent);
  backdrop-filter: saturate(150%) blur(10px);
  border-bottom: 1px solid var(--border);
}
.nav { max-width: var(--maxw); margin: 0 auto; padding: .8rem var(--gutter); display: flex; align-items: center; justify-content: space-between; gap: 1rem; }
.nav__brand { display: inline-flex; align-items: center; gap: .6rem; color: var(--text); font-family: var(--font-serif); font-weight: 600; }
.nav__brand:hover { color: var(--text); }
.nav__brand-mark { display: grid; place-items: center; width: 34px; height: 34px; font-size: 1.25rem; line-height: 1; }
.nav__brand-name { font-size: 1.05rem; }
.nav__menu { list-style: none; display: flex; align-items: center; gap: 1.4rem; margin: 0; padding: 0; }
.nav__menu > li > a { color: var(--text-soft); font-size: .94rem; font-weight: 500; padding: .25rem 0; position: relative; }
.nav__menu > li > a::after { content: ""; position: absolute; left: 0; bottom: -3px; width: 0; height: 2px; background: var(--accent); transition: width var(--transition); }
.nav__menu > li > a:hover { color: var(--text); }
.nav__menu > li > a:hover::after { width: 100%; }
.nav__menu > li > a[aria-current="location"] { color: var(--text); }
.nav__menu > li > a[aria-current="location"]::after { width: 100%; }

.nav__toggle { display: none; flex-direction: column; justify-content: center; gap: 5px; width: 42px; height: 42px; padding: 0 9px; background: transparent; border: 1px solid var(--border-strong); border-radius: var(--radius-sm); cursor: pointer; }
.nav__toggle span { height: 2px; width: 100%; background: var(--text); border-radius: 2px; transition: transform var(--transition), opacity var(--transition); }
.nav__toggle[aria-expanded="true"] span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav__toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav__toggle[aria-expanded="true"] span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

.theme-toggle { display: grid; place-items: center; width: 38px; height: 38px; background: var(--bg-elev); border: 1px solid var(--border-strong); border-radius: 9px; color: var(--text); cursor: pointer; font-size: 1.05rem; transition: border-color var(--transition); }
.theme-toggle:hover { border-color: var(--accent); }
.ic--moon { display: none; }
[data-theme="dark"] .ic--sun { display: none; }
[data-theme="dark"] .ic--moon { display: block; }

/* ---- Layout ---- */
.hero__inner, .section { max-width: var(--maxw); margin: 0 auto; padding-left: var(--gutter); padding-right: var(--gutter); }
.section { padding-top: clamp(3.25rem, 7vw, 5.5rem); }
.section:last-of-type { padding-bottom: clamp(3.25rem, 7vw, 5.5rem); }
:target, .section, .hero, #main, #top { scroll-margin-top: calc(var(--header-h) + 1rem); }
.section__head { display: flex; align-items: baseline; gap: .85rem; margin-bottom: 2rem; padding-bottom: .8rem; border-bottom: 1px solid var(--border); }
.section__index { font-family: var(--font-mono); font-size: .78rem; letter-spacing: .1em; color: var(--accent); }
.section__title { font-family: var(--font-serif); font-size: clamp(1.5rem, 3.5vw, 2.1rem); font-weight: 600; }

/* ---- Hero ---- */
.hero { padding-top: clamp(2.5rem, 6vw, 4.5rem); padding-bottom: clamp(1rem, 3vw, 2rem); }
.hero__inner { display: grid; grid-template-columns: 1.55fr 0.85fr; gap: clamp(2rem, 5vw, 3.5rem); align-items: center; }
.hero__eyebrow { font-family: var(--font-mono); font-size: .8rem; letter-spacing: .14em; text-transform: uppercase; color: var(--text-faint); margin-bottom: 1rem; }
.hero__name { font-family: var(--font-serif); font-size: clamp(2.6rem, 6.5vw, 4rem); font-weight: 600; letter-spacing: -0.015em; }
.hero__alias { color: var(--text-faint); font-style: italic; font-weight: 400; }
.hero__title { margin-top: .5rem; font-size: clamp(1.1rem, 2.4vw, 1.35rem); color: var(--accent); font-weight: 600; }
.hero__lede { margin-top: 1.3rem; max-width: 40rem; font-size: clamp(1rem, 1.4vw, 1.12rem); color: var(--text-soft); }

.hero__actions { margin-top: 1.9rem; display: flex; flex-wrap: wrap; gap: .8rem; }
.btn { display: inline-flex; align-items: center; gap: .5rem; padding: .7rem 1.35rem; border-radius: 999px; font-weight: 600; font-size: .95rem; border: 1px solid transparent; transition: background var(--transition), border-color var(--transition), color var(--transition), transform var(--transition); }
.btn .ic { width: 1.05em; height: 1.05em; }
.btn--primary { background: var(--accent); color: var(--on-accent); }
.btn--primary:hover { background: var(--accent-soft); color: var(--on-accent); transform: translateY(-1px); }
.btn--ghost { border-color: var(--border-strong); color: var(--text); }
.btn--ghost:hover { border-color: var(--accent); color: var(--accent); transform: translateY(-1px); }

.social { margin-top: 1.8rem; padding: 0; list-style: none; display: flex; flex-wrap: wrap; gap: .6rem 1.4rem; }
.social a { display: inline-flex; align-items: center; gap: .45rem; color: var(--text-soft); font-size: .9rem; font-weight: 500; }
.social a .ic { width: 1.1em; height: 1.1em; color: var(--text-faint); transition: color var(--transition); }
.social a:hover { color: var(--accent); }
.social a:hover .ic { color: var(--accent); }

/* Portrait — original proportions, softly rounded corners (no ellipse) */
.hero__portrait { display: flex; justify-content: center; }
.portrait { margin: 0; width: min(300px, 70vw); }
.portrait img {
  width: 100%; height: auto; display: block;
  border-radius: var(--radius); border: 1px solid var(--border-strong);
  box-shadow: var(--shadow);
}

/* ---- About ---- */
.about { display: grid; grid-template-columns: 1.6fr 1fr; gap: clamp(1.5rem, 4vw, 3rem); align-items: start; }
.about__body p + p { margin-top: 1.1rem; }
.about__body p { font-size: 1.04rem; color: var(--text-soft); }
.about__body .lead { font-family: var(--font-serif); font-size: 1.24rem; line-height: 1.5; color: var(--text); }
.about__facts { background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius); padding: 1.5rem; box-shadow: var(--shadow); }
.about__facts dl { margin: 0; }
.fact + .fact { margin-top: 1.05rem; padding-top: 1.05rem; border-top: 1px solid var(--border); }
.fact dt { font-family: var(--font-mono); font-size: .7rem; letter-spacing: .1em; text-transform: uppercase; color: var(--text-faint); margin-bottom: .3rem; }
.fact dd { margin: 0; font-size: .94rem; color: var(--text); }
.fact__list { list-style: none; margin: 0; padding: 0; display: grid; gap: .35rem; }
.fact__list li { font-size: .94rem; color: var(--text); line-height: 1.4; }

/* ---- Research cards ---- */
.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 1.1rem; }
.card { background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius); padding: 1.4rem; transition: transform var(--transition), border-color var(--transition), box-shadow var(--transition); }
.card:hover { transform: translateY(-2px); border-color: var(--border-strong); box-shadow: var(--shadow); }
.card__title { font-family: var(--font-serif); font-size: 1.16rem; margin-bottom: .5rem; }
.card p { color: var(--text-soft); font-size: .95rem; }

/* ---- Publications ---- */
.pubs__bar { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 1rem; margin-bottom: 1.6rem; }
.filters { display: flex; flex-wrap: wrap; gap: .5rem; }
.filter { padding: .42rem 1rem; border-radius: 999px; border: 1px solid var(--border-strong); background: transparent; color: var(--text-soft); font-family: var(--font-sans); font-size: .86rem; font-weight: 500; cursor: pointer; transition: color var(--transition), border-color var(--transition), background var(--transition); }
.filter:hover { border-color: var(--accent); color: var(--text); }
.filter.is-active { background: var(--accent); border-color: var(--accent); color: var(--on-accent); }
.scholar-link { display: inline-flex; align-items: center; gap: .4rem; font-size: .86rem; font-weight: 500; color: var(--text-soft); }
.scholar-link:hover { color: var(--accent); }

.pubs { list-style: none; margin: 0; padding: 0; }
.pub { display: grid; grid-template-columns: 130px 1fr; gap: 1.4rem; padding: 1.3rem 0; border-top: 1px solid var(--border); transition: background var(--transition); }
.pub:first-child { border-top: none; }
.pub[hidden] { display: none; }
.pub__year { display: flex; flex-direction: column; gap: .15rem; padding-top: .15rem; }
.pub__year span { font-family: var(--font-mono); font-size: 1.05rem; font-weight: 500; color: var(--text); }
.pub__year em { font-style: normal; font-size: .82rem; font-weight: 600; color: var(--accent); }
.pub__title { font-family: var(--font-serif); font-size: 1.2rem; line-height: 1.35; margin-bottom: .4rem; }
.pub__authors { font-size: .92rem; color: var(--text-soft); }
.pub__authors strong { color: var(--text); font-weight: 600; }
.pub__note { margin-top: .5rem; font-size: .8rem; color: var(--text-faint); font-style: italic; }
.pub__links { margin-top: .8rem; display: flex; flex-wrap: wrap; gap: .5rem; }
.pub__links a { display: inline-flex; align-items: center; gap: .35rem; font-size: .84rem; font-weight: 500; color: var(--text-soft); padding: .32rem .7rem; border: 1px solid var(--border); border-radius: 999px; background: var(--bg-elev); transition: color var(--transition), border-color var(--transition), background var(--transition); }
.pub__links a:hover { color: var(--accent); border-color: var(--accent); background: var(--accent-tint); }
.pub__links a .ic { width: 1.05em; height: 1.05em; }
.pubs__empty { margin-top: 1.5rem; color: var(--text-faint); font-style: italic; }

/* ---- Timeline ---- */
.timeline-group + .timeline-group { margin-top: 2.4rem; }
.timeline-group__label { font-family: var(--font-mono); font-size: .76rem; letter-spacing: .14em; text-transform: uppercase; color: var(--text-faint); margin-bottom: 1.3rem; }
.timeline { list-style: none; margin: 0; padding: 0 0 0 1.5rem; border-left: 2px solid var(--border); display: grid; gap: 1.7rem; }
.timeline__item { position: relative; }
.timeline__item::before { content: ""; position: absolute; left: calc(-1.5rem - 6px); top: .45rem; width: 11px; height: 11px; border-radius: 50%; background: var(--accent); border: 2px solid var(--bg); }
.timeline__date { font-family: var(--font-mono); font-size: .8rem; color: var(--text-faint); }
.timeline__title { font-family: var(--font-serif); font-size: 1.12rem; margin-top: .25rem; }
.timeline__org { color: var(--text-soft); font-size: .94rem; margin-top: .15rem; }
.timeline__note { color: var(--text-soft); font-size: .89rem; margin-top: .35rem; }

/* ---- Contact ---- */
.contact { display: grid; grid-template-columns: 1fr 1fr; gap: clamp(1.5rem, 4vw, 3rem); align-items: start; }
.contact__lede { font-size: 1.14rem; color: var(--text-soft); font-family: var(--font-serif); line-height: 1.5; }
.contact__links { list-style: none; margin: 0; padding: 0; display: grid; gap: .85rem; }
.contact__links li { display: flex; align-items: baseline; gap: 1rem; padding-bottom: .85rem; border-bottom: 1px solid var(--border); }
.contact__label { display: inline-flex; align-items: center; gap: .45rem; font-family: var(--font-mono); font-size: .72rem; letter-spacing: .08em; text-transform: uppercase; color: var(--text-faint); min-width: 7rem; }
.contact__label .ic { color: var(--accent); width: 1.1em; height: 1.1em; }
.contact__links a { font-weight: 500; overflow-wrap: anywhere; }

/* ---- Footer ---- */
.site-footer { max-width: var(--maxw); margin: clamp(2.5rem, 5vw, 4rem) auto 0; padding: 2.2rem var(--gutter); border-top: 1px solid var(--border); display: flex; flex-wrap: wrap; gap: 1rem; justify-content: space-between; align-items: center; color: var(--text-faint); font-size: .87rem; }
.site-footer__top { font-weight: 600; }

/* ---- Responsive ---- */
@media (max-width: 860px) {
  .hero__inner { grid-template-columns: 1fr; }
  .hero__portrait { order: -1; justify-content: flex-start; }
  .portrait { width: min(200px, 48vw); }
  .about { grid-template-columns: 1fr; }
  .contact { grid-template-columns: 1fr; }
}
@media (max-width: 720px) {
  .js .nav__toggle { display: flex; }
  .js .nav__menu { position: fixed; inset: var(--header-h) 0 auto 0; flex-direction: column; align-items: flex-start; gap: .3rem; background: var(--bg-elev); border-bottom: 1px solid var(--border); padding: 1rem var(--gutter) 1.5rem; transform: translateY(-120%); transition: transform 260ms ease; box-shadow: var(--shadow); }
  .js .nav__menu.is-open { transform: translateY(0); }
  .nav__menu > li { width: 100%; }
  .nav__menu > li > a { display: block; padding: .6rem 0; font-size: 1rem; }
  .theme-toggle { margin-top: .4rem; }
  .pub { grid-template-columns: 1fr; gap: .5rem; }
  .pub__year { flex-direction: row; align-items: baseline; gap: .6rem; }
}