/* ============================================================
   Jinghao Chen — personal site
   Tokens → base → layout → components → responsive
   ============================================================ */

/* ---------- 1. Tokens ---------- */
:root {
  --paper: #f8f6f2;
  --paper-raised: #fffefb;
  --ink: #191a17;
  --ink-soft: #45463f;
  --muted: #6d6d64;
  --rule: #e3dfd6;
  --rule-strong: #cfcabf;
  --accent: #0f5f57;
  --accent-ink: #ffffff;
  --accent-wash: rgba(15, 95, 87, 0.07);
  --focus: #1b62c9;

  --serif: "Iowan Old Style", "Palatino Linotype", "Book Antiqua", Palatino,
    Georgia, "Times New Roman", serif;
  --sans: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "Cascadia Code", "SF Mono", Consolas,
    "Liberation Mono", monospace;

  --page: 76rem;
  --rail: 40rem;
  --gutter: clamp(1.25rem, 4vw, 3rem);
  --radius: 14px;
  --header-h: 5.5rem;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #0f1110;
    --paper-raised: #161a18;
    --ink: #edebe4;
    --ink-soft: #cfcdc5;
    --muted: #9d9b93;
    --rule: #262a27;
    --rule-strong: #363b37;
    --accent: #6ecfc2;
    --accent-ink: #08201d;
    --accent-wash: rgba(110, 207, 194, 0.09);
    --focus: #7fb2ff;
  }
}

:root[data-theme="dark"] {
  --paper: #0f1110;
  --paper-raised: #161a18;
  --ink: #edebe4;
  --ink-soft: #cfcdc5;
  --muted: #9d9b93;
  --rule: #262a27;
  --rule-strong: #363b37;
  --accent: #6ecfc2;
  --accent-ink: #08201d;
  --accent-wash: rgba(110, 207, 194, 0.09);
  --focus: #7fb2ff;
}

/* ---------- 2. Base ---------- */
*,
*::before,
*::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 1.5rem);
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1rem;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  overflow-x: hidden;
}

h1, h2, h3, h4 {
  margin: 0;
  font-weight: 600;
  line-height: 1.2;
  text-wrap: balance;
}

p { margin: 0 0 1rem; }
p:last-child { margin-bottom: 0; }

a {
  color: inherit;
  text-decoration-color: var(--rule-strong);
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
  transition: color 140ms ease, text-decoration-color 140ms ease;
}

a:hover {
  color: var(--accent);
  text-decoration-color: currentColor;
}

code {
  font-family: var(--mono);
  font-size: 0.875em;
  padding: 0.1em 0.35em;
  border-radius: 5px;
  background: var(--accent-wash);
  color: var(--ink);
}

:focus-visible {
  outline: 2.5px solid var(--focus);
  outline-offset: 3px;
  border-radius: 3px;
}

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

/* ---------- 3. Header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  border-bottom: 1px solid transparent;
  backdrop-filter: saturate(140%) blur(12px);
  -webkit-backdrop-filter: saturate(140%) blur(12px);
  transition: border-color 180ms ease, background 180ms ease;
}

.site-header.is-stuck {
  border-bottom-color: var(--rule);
  background: color-mix(in srgb, var(--paper) 94%, transparent);
}

.header-inner {
  max-width: var(--page);
  margin: 0 auto;
  padding: 0 var(--gutter);
  height: var(--header-h);
  display: flex;
  align-items: center;
  gap: 1.5rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.85rem;
  text-decoration: none;
  font-weight: 600;
  font-size: 1.0625rem;
  letter-spacing: -0.01em;
  white-space: nowrap;
}

.brand-mark {
  display: block;
  flex: none;
  width: 4rem;
  height: 4rem;
  border-radius: 50%;
  object-fit: cover;
  background: var(--paper-raised);
  transition: transform 160ms ease;
}

.brand:hover .brand-mark { transform: scale(1.06); }

.nav {
  display: flex;
  align-items: center;
  gap: 1.4rem;
  margin-left: auto;
  font-size: 0.9375rem;
}

.nav a {
  text-decoration: none;
  color: var(--muted);
  padding: 0.25rem 0;
  border-bottom: 1.5px solid transparent;
  transition: color 140ms ease, border-color 140ms ease;
}

.nav a:hover { color: var(--ink); }

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

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

/* ---------- 4. Buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  padding: 0.62rem 1.15rem;
  border: 1px solid var(--ink);
  border-radius: 999px;
  background: var(--ink);
  color: var(--paper);
  font-size: 0.9rem;
  font-weight: 500;
  line-height: 1.3;
  text-decoration: none;
  white-space: nowrap;
  transition: background 150ms ease, color 150ms ease,
    border-color 150ms ease, transform 120ms ease;
}

.btn:hover {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-ink);
}

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

.btn-ghost {
  background: transparent;
  color: var(--ink);
  border-color: var(--rule-strong);
}

.btn-ghost:hover {
  background: var(--ink);
  border-color: var(--ink);
  color: var(--paper);
}

.btn-small {
  padding: 0.42rem 0.9rem;
  font-size: 0.8125rem;
}

.btn-github { gap: 0.45rem; }

.btn-github .gh-icon {
  width: 1.05rem;
  height: 1.05rem;
  flex: none;
  fill: currentColor;
}

.btn-linkedin { gap: 0.45rem; }

.btn-linkedin .li-icon {
  width: 1.1rem;
  height: 1.1rem;
  flex: none;
}

/* ---------- 5. Theme toggle ---------- */
.theme-toggle {
  display: inline-grid;
  place-items: center;
  width: 2.5rem;
  height: 2.5rem;
  padding: 0;
  color: var(--muted);
  background: transparent;
  border: 1px solid var(--rule);
  border-radius: 50%;
  cursor: pointer;
  transition: color 150ms ease, border-color 150ms ease,
    background 150ms ease;
}

.theme-toggle:hover {
  color: var(--ink);
  border-color: var(--rule-strong);
  background: var(--paper-raised);
}

.theme-toggle .icon {
  width: 1rem;
  height: 1rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.6;
  stroke-linecap: round;
}

/* Moon in light mode (click for dark), sun in dark mode. */
.icon-sun { display: none; }
.icon-moon { display: block; }

:root[data-theme="dark"] .icon-sun,
.theme-toggle.is-dark .icon-sun { display: block; }

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

/* ---------- 6. Layout shell ---------- */
main {
  max-width: var(--page);
  margin: 0 auto;
  padding: 0 var(--gutter) 4rem;
}

/* ---------- 7. Hero ---------- */
.hero {
  padding: clamp(3rem, 9vw, 6.5rem) 0 clamp(1rem, 2vw, 1.5rem);
}

/* The hero now ends with the story, so the first section does not need its
   full top padding on top of the hero's own bottom spacing. */
.hero + .section {
  padding-top: clamp(1.5rem, 2.5vw, 2rem);
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  margin: 0 0 1.5rem;
  font-family: var(--mono);
  font-size: 0.75rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
}

.dot-live {
  width: 0.45rem;
  height: 0.45rem;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-wash);
}

.hero h1 {
  font-family: var(--serif);
  font-size: clamp(2.9rem, 1.9rem + 4.6vw, 5.1rem);
  font-weight: 500;
  letter-spacing: -0.032em;
  line-height: 0.98;
  margin-bottom: 1.5rem;
  max-width: 22ch;
}

.h1-alt {
  font-style: italic;
  font-weight: 400;
  color: var(--muted);
}

.lede {
  font-size: clamp(1.0625rem, 0.98rem + 0.4vw, 1.28rem);
  line-height: 1.6;
  color: var(--ink-soft);
  max-width: 46ch;
}

.hero-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7rem;
  margin: 2rem 0 0;
}

.stats {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 1.5rem;
  margin: clamp(2.5rem, 6vw, 4rem) 0 0;
  padding-top: 1.5rem;
  border-top: 1px solid var(--rule);
}

.stat dt {
  font-size: 0.75rem;
  line-height: 1.4;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--muted);
}

.stat dd {
  margin: 0.35rem 0 0;
  font-family: var(--serif);
  font-size: clamp(1.35rem, 1.1rem + 0.7vw, 1.75rem);
  font-weight: 500;
  letter-spacing: -0.02em;
}

/* ---------- 7b. Hero story ---------- */
.story {
  margin-top: clamp(3rem, 6.5vw, 4.5rem);
  padding-top: clamp(2rem, 4vw, 2.75rem);
  border-top: 1px solid var(--rule);
}

.story-title {
  margin-bottom: clamp(1.25rem, 2.5vw, 1.75rem);
  font-family: var(--mono);
  font-size: 0.6875rem;
  font-weight: 600;
  letter-spacing: 0.09em;
  text-transform: uppercase;
  color: var(--muted);
}

.story p {
  margin: 0 0 1.5rem;
  font-size: 1rem;
  line-height: 1.65;
  color: var(--ink-soft);
}

.story blockquote {
  margin: 0 0 1.75rem;
  padding: 0.25rem 0 0.25rem clamp(1rem, 2vw, 1.75rem);
  border-left: 2px solid var(--accent);
}

.story blockquote p {
  margin: 0;
  font-family: var(--serif);
  font-size: clamp(1.4rem, 1rem + 1.5vw, 2.15rem);
  line-height: 1.32;
  letter-spacing: -0.02em;
  color: var(--ink);
  text-wrap: balance;
}

.story p.story-outro { margin-bottom: 0; }

/* ---------- 8. Sections ---------- */
.section {
  display: grid;
  grid-template-columns: 11rem minmax(0, 1fr);
  gap: clamp(1.5rem, 4vw, 4rem);
  padding: clamp(2.75rem, 5vw, 4rem) 0;
  border-top: 1px solid var(--rule);
}

.section-label {
  position: sticky;
  top: calc(var(--header-h) + 2.5rem);
  align-self: start;
}

.section-num {
  display: block;
  margin-bottom: 0.4rem;
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--muted);
  letter-spacing: 0.08em;
}

.section-label h2 {
  font-size: 0.8125rem;
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink);
}

.section-body {
  min-width: 0;
  max-width: var(--rail);
}

.section-intro {
  max-width: none;
  color: var(--ink-soft);
  margin-bottom: 2.25rem;
}

.prose {
  max-width: none;
  color: var(--ink-soft);
  margin-bottom: 1.15rem;
}

.prose:last-child { margin-bottom: 0; }

.subhead {
  margin: 3rem 0 1.5rem;
  font-size: 0.8125rem;
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--muted);
}

.section-body > .subhead:first-child { margin-top: 0; }

/* ---------- 9. Pillars ---------- */
.pillars {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1px;
  margin: 2.5rem 0 0;
  padding: 0;
  list-style: none;
  background: var(--rule);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  overflow: hidden;
}

.pillars li {
  padding: 1.5rem 1.35rem;
  background: var(--paper);
}

.pillars h3 {
  margin-bottom: 0.5rem;
  font-size: 0.95rem;
  font-weight: 600;
}

.pillars p {
  margin: 0;
  font-size: 0.875rem;
  line-height: 1.6;
  color: var(--muted);
}

/* ---------- 10. Toolkit ---------- */
.skill-strip {
  margin: 0 0 1.35rem;
}

.skill-strip img {
  display: block;
  width: 100%;
  height: auto;
  max-width: 40rem;
}

.toolkit {
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0;
}

.toolkit > div {
  display: grid;
  grid-template-columns: 6.5rem minmax(0, 1fr);
  gap: 1rem;
  padding: 0.85rem 0;
  border-top: 1px solid var(--rule);
}

.toolkit > div:last-child { border-bottom: 1px solid var(--rule); }

.toolkit dt {
  padding-top: 0.3rem;
  font-family: var(--mono);
  font-size: 0.6875rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--muted);
}

.toolkit dd {
  margin: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.toolkit span {
  padding: 0.2rem 0.6rem;
  font-size: 0.8125rem;
  line-height: 1.5;
  color: var(--ink-soft);
  background: var(--paper-raised);
  border: 1px solid var(--rule);
  border-radius: 999px;
}

/* ---------- 11. Projects ---------- */
.project {
  padding: clamp(1.35rem, 3vw, 2rem);
  margin-bottom: 1rem;
  background: var(--paper-raised);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  transition: border-color 180ms ease, transform 180ms ease;
}

.project:hover { border-color: var(--rule-strong); }

.project-featured {
  border-color: var(--rule-strong);
  box-shadow: 0 1px 0 var(--rule), 0 14px 34px -28px rgba(0, 0, 0, 0.55);
}

.project-head { margin-bottom: 0.85rem; }

.project h3 {
  font-family: var(--serif);
  font-size: clamp(1.3rem, 1.1rem + 0.6vw, 1.6rem);
  font-weight: 500;
  letter-spacing: -0.02em;
  margin-bottom: 0.35rem;
}

.project-meta {
  margin: 0;
  font-family: var(--mono);
  font-size: 0.6875rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--muted);
}

.project > p {
  max-width: none;
  color: var(--ink-soft);
  font-size: 0.95rem;
}

.project-points {
  margin: 1rem 0 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 0.45rem;
  max-width: none;
}

.project-points li {
  position: relative;
  padding-left: 1.1rem;
  font-size: 0.9rem;
  line-height: 1.55;
  color: var(--muted);
}

.project-points li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.62em;
  width: 0.4rem;
  height: 1px;
  background: var(--accent);
}

.links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem 1.25rem;
  margin: 1.35rem 0 0;
  padding: 0;
  list-style: none;
  font-size: 0.8125rem;
}

.links a {
  text-decoration: none;
  color: var(--accent);
  font-weight: 500;
}

.links a:hover { text-decoration: underline; }

/* ---------- 11. Timeline ---------- */
.timeline {
  margin: 0;
  padding: 0;
  list-style: none;
}

.timeline > li {
  padding-bottom: 1.75rem;
  margin-bottom: 1.75rem;
  border-bottom: 1px solid var(--rule);
}

.timeline > li:last-child {
  border-bottom: 0;
  margin-bottom: 0;
  padding-bottom: 0;
}

.entry-head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.25rem 1rem;
}

.entry-head h3,
.entry-head h4 {
  font-size: 1.0625rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.entry-when {
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--muted);
  white-space: nowrap;
}

.entry-org {
  margin: 0.2rem 0 0.7rem;
  font-size: 0.875rem;
  color: var(--muted);
}

.timeline ul {
  margin: 0;
  padding-left: 1.05rem;
  display: grid;
  gap: 0.35rem;
  max-width: none;
}

.timeline li li {
  font-size: 0.9rem;
  line-height: 1.6;
  color: var(--ink-soft);
}

.timeline-compact > li {
  border-bottom: 0;
  margin-bottom: 1rem;
  padding-bottom: 0;
}

/* ---------- 12. Details / disclosure ---------- */
.earlier {
  margin-top: 1.5rem;
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  background: var(--paper-raised);
}

.earlier summary {
  position: relative;
  padding: 0.9rem 3rem 0.9rem 1.15rem;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--ink);
  cursor: pointer;
  list-style: none;
  user-select: none;
}

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

.earlier summary::after {
  content: "+";
  position: absolute;
  right: 1.15rem;
  top: 50%;
  transform: translateY(-50%);
  font-family: var(--mono);
  font-size: 1rem;
  color: var(--muted);
  transition: transform 180ms ease;
}

.earlier[open] summary::after { transform: translateY(-50%) rotate(45deg); }

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

.earlier-list {
  margin: 0;
  padding: 0 1.15rem 1.15rem;
  list-style: none;
  display: grid;
  gap: 0.85rem;
  border-top: 1px solid var(--rule);
  padding-top: 1.15rem;
}

.earlier-list li {
  font-size: 0.875rem;
  color: var(--ink-soft);
  display: grid;
  gap: 0.1rem;
}

.earlier-list strong { color: var(--ink); font-weight: 600; }

.earlier-list span {
  font-size: 0.8125rem;
  color: var(--muted);
  line-height: 1.55;
}

/* ---------- 13. Certifications ---------- */
.certs {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.7rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.certs li {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
  padding: 0.85rem 1rem;
  min-height: 4.75rem;
  background: var(--paper-raised);
  border: 1px solid var(--rule);
  border-radius: 10px;
}

.certs strong {
  font-size: 0.85rem;
  font-weight: 600;
  line-height: 1.35;
  letter-spacing: -0.005em;
}

.certs span {
  margin-top: auto;
  font-family: var(--mono);
  font-size: 0.6875rem;
  letter-spacing: 0.02em;
  color: var(--muted);
}

.cert-group + .cert-group { margin-top: 2.1rem; }

.cert-group-title {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin: 0 0 0.85rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--rule);
  font-family: var(--mono);
  font-size: 0.6875rem;
  font-weight: 600;
  letter-spacing: 0.09em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.cert-count {
  padding: 0.05rem 0.42rem;
  font-size: 0.625rem;
  font-weight: 500;
  letter-spacing: 0;
  color: var(--muted);
  border: 1px solid var(--rule);
  border-radius: 999px;
}

/* ---------- 14. Publication ---------- */
.paper {
  padding: 1.4rem 1.5rem;
  background: var(--paper-raised);
  border: 1px solid var(--rule);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius) var(--radius) 0;
}

.paper h4 {
  font-family: var(--serif);
  font-size: 1.05rem;
  font-weight: 500;
  letter-spacing: -0.01em;
  line-height: 1.35;
  margin-bottom: 0.4rem;
}

.paper-meta {
  margin: 0 0 0.7rem;
  font-family: var(--mono);
  font-size: 0.6875rem;
  line-height: 1.5;
  letter-spacing: 0.02em;
  color: var(--muted);
}

.paper p {
  max-width: none;
  font-size: 0.9rem;
  color: var(--ink-soft);
}

.paper p:last-child { margin-top: 0.6rem; }

.paper a {
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--accent);
  text-decoration: none;
}

.paper a:hover { text-decoration: underline; }

.awards {
  margin: 1rem 0 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 0.8rem;
}

.awards li {
  position: relative;
  padding-left: 1.1rem;
  font-size: 0.9rem;
  line-height: 1.55;
}

.awards li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.62em;
  width: 0.4rem;
  height: 1px;
  background: var(--accent);
}

.awards strong { font-weight: 600; }

.awards li > span {
  display: block;
  font-size: 0.8125rem;
  color: var(--muted);
}

.award-link {
  display: inline-block;
  margin-top: 0.25rem;
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--accent);
  text-decoration: none;
}

.award-link:hover { text-decoration: underline; }

/* ---------- 15. Contact ---------- */
.contact-cards {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.9rem;
  margin-top: 1.75rem;
}

.contact-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.55rem;
  padding: 1.9rem 1rem;
  text-align: center;
  text-decoration: none;
  color: var(--ink);
  background: var(--paper-raised);
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  transition: border-color 180ms ease, transform 180ms ease,
    box-shadow 180ms ease;
}

.contact-card:hover {
  color: var(--ink);
  border-color: var(--rule-strong);
  transform: translateY(-2px);
  box-shadow: 0 18px 32px -28px rgba(0, 0, 0, 0.65);
}

.contact-icon {
  display: grid;
  place-items: center;
  width: 3.25rem;
  height: 3.25rem;
  margin-bottom: 0.15rem;
  color: var(--ink);
  background: var(--paper);
  border: 1px solid var(--rule);
  border-radius: 50%;
  transition: background 180ms ease, color 180ms ease,
    border-color 180ms ease;
}

.contact-icon svg {
  width: 1.5rem;
  height: 1.5rem;
}

.contact-card:hover .contact-icon {
  color: var(--paper);
  background: var(--ink);
  border-color: var(--ink);
}

.contact-label {
  font-size: 0.9375rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.contact-handle {
  font-family: var(--mono);
  font-size: 0.6875rem;
  letter-spacing: 0.02em;
  color: var(--muted);
  word-break: break-word;
}

/* ---------- 16. Back to top ---------- */
.to-top {
  position: fixed;
  right: clamp(0.9rem, 3vw, 2rem);
  bottom: clamp(0.9rem, 3vw, 2rem);
  z-index: 40;
  display: grid;
  place-items: center;
  width: 2.75rem;
  height: 2.75rem;
  color: var(--ink);
  background: var(--paper-raised);
  border: 1px solid var(--rule-strong);
  border-radius: 50%;
  box-shadow: 0 12px 26px -16px rgba(0, 0, 0, 0.55);
  opacity: 0;
  visibility: hidden;
  transform: translateY(0.55rem);
  transition: opacity 180ms ease, transform 180ms ease,
    visibility 180ms ease, background 150ms ease, border-color 150ms ease,
    color 150ms ease;
}

.to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: none;
}

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

.to-top svg {
  width: 1.1rem;
  height: 1.1rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.8;
  stroke-linecap: round;
  stroke-linejoin: round;
}

/* ---------- 17. Footer ---------- */
.site-footer {
  max-width: var(--page);
  margin: 0 auto;
  /* Side padding keeps the footer clear of the fixed greeter and back-to-top. */
  padding: 2rem calc(var(--gutter) + 3.5rem) 3rem calc(var(--gutter) + 3.5rem);
  border-top: 1px solid var(--rule);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.5rem;
  font-size: 0.8125rem;
  color: var(--muted);
}

.site-footer p { margin: 0; }

.footer-note { color: var(--muted); }

/* ---------- 17. Skip link ---------- */
.skip-link {
  position: absolute;
  left: 0;
  top: -100px;
  z-index: 100;
  padding: 0.7rem 1.1rem;
  background: var(--ink);
  color: var(--paper);
  border-radius: 0 0 var(--radius) 0;
  text-decoration: none;
  font-size: 0.875rem;
  transition: top 160ms ease;
}

.skip-link:focus { top: 0; }

/* ---------- 18. Responsive ---------- */
@media (max-width: 56rem) {
  .header-inner { gap: 1rem; }

  .brand {
    gap: 0.7rem;
    font-size: 1rem;
  }

  .nav {
    gap: 1rem;
    font-size: 0.875rem;
  }

  .theme-toggle {
    width: 2.25rem;
    height: 2.25rem;
  }
}

@media (max-width: 60rem) {
  .section {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }

  .section-label {
    position: static;
    display: flex;
    align-items: baseline;
    gap: 0.75rem;
  }

  .section-num { margin-bottom: 0; }

  .pillars { grid-template-columns: 1fr; }

  .certs { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 46rem) {
  .nav { display: none; }

  .toolkit > div {
    grid-template-columns: 1fr;
    gap: 0.4rem;
  }

  .toolkit dt { padding-top: 0; }

  .header-actions { margin-left: auto; }

  .stats {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 1.25rem 1rem;
  }

  .hero { padding-top: 2.5rem; }

  .hero h1 { max-width: none; }

  .certs { grid-template-columns: 1fr; }

  .certs li { min-height: 0; }

  .site-footer { flex-direction: column; }
}

@media (max-width: 30rem) {
  .brand-name { display: none; }

  .stats { grid-template-columns: 1fr 1fr; }

  .contact-cards { grid-template-columns: 1fr; }
}

/* ---------- 20. Error page (404.html) ---------- */
.error-page {
  max-width: var(--rail);
  margin: 0 auto;
  padding: clamp(4rem, 12vh, 9rem) var(--gutter) 5rem;
}

.error-page h1 {
  margin-bottom: 1rem;
  font-family: var(--serif);
  font-size: clamp(2.4rem, 1.6rem + 3vw, 3.6rem);
  font-weight: 500;
  letter-spacing: -0.03em;
  line-height: 1.05;
}

.error-page .prose { margin-bottom: 1.75rem; }

.error-actions { margin: 0; }

/* ---------- 21. Greeter ---------- */
.greeter {
  position: fixed;
  left: clamp(0.9rem, 3vw, 2rem);
  bottom: clamp(0.9rem, 3vw, 2rem);
  z-index: 40;
  display: flex;
  align-items: flex-end;
  gap: 0.7rem;
  max-width: calc(100vw - 1.8rem);
}

.greeter-avatar {
  flex: none;
  width: 3.25rem;
  height: 3.25rem;
  padding: 0;
  overflow: hidden;
  background: var(--paper-raised);
  border: 1px solid var(--rule-strong);
  border-radius: 50%;
  box-shadow: 0 12px 26px -16px rgba(0, 0, 0, 0.55);
  cursor: pointer;
  transition: transform 160ms ease, border-color 160ms ease;
}

.greeter-avatar img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.greeter-avatar:hover {
  transform: translateY(-2px) scale(1.05);
  border-color: var(--accent);
}

.greeter-bubble {
  position: relative;
  max-width: 17rem;
  margin-bottom: 0.35rem;
  padding: 0.8rem 2.1rem 0.8rem 1rem;
  background: var(--paper-raised);
  border: 1px solid var(--rule-strong);
  border-radius: 14px;
  box-shadow: 0 18px 34px -26px rgba(0, 0, 0, 0.6);
  font-size: 0.8125rem;
  line-height: 1.5;
  color: var(--ink-soft);
  opacity: 0;
  visibility: hidden;
  transform: translateY(0.4rem) scale(0.97);
  transform-origin: bottom left;
  transition: opacity 220ms ease, transform 220ms ease,
    visibility 220ms ease;
}

.greeter.is-open .greeter-bubble {
  opacity: 1;
  visibility: visible;
  transform: none;
}

.greeter-bubble::before {
  content: "";
  position: absolute;
  left: -5px;
  bottom: 16px;
  width: 9px;
  height: 9px;
  background: var(--paper-raised);
  border-left: 1px solid var(--rule-strong);
  border-bottom: 1px solid var(--rule-strong);
  transform: rotate(45deg);
}

.greeter-text { margin: 0; }

.greeter-contact {
  display: flex;
  flex-wrap: wrap;
  gap: 0.3rem 0.8rem;
  margin: 0.55rem 0 0;
  padding-top: 0.5rem;
  border-top: 1px solid var(--rule);
  font-size: 0.75rem;
  font-weight: 500;
}

.greeter-contact a {
  color: var(--accent);
  text-decoration: none;
}

.greeter-contact a:hover { text-decoration: underline; }

.greeter-close {
  position: absolute;
  top: 0.3rem;
  right: 0.35rem;
  display: grid;
  place-items: center;
  width: 1.4rem;
  height: 1.4rem;
  padding: 0;
  font-size: 1rem;
  line-height: 1;
  color: var(--muted);
  background: transparent;
  border: 0;
  border-radius: 50%;
  cursor: pointer;
}

.greeter-close:hover {
  color: var(--ink);
  background: var(--accent-wash);
}

/* One small wave when the bubble opens. */
.greeter.is-open .greeter-avatar {
  animation: greeter-wave 700ms ease-in-out 1;
}

@keyframes greeter-wave {
  0%, 100% { transform: rotate(0deg); }
  25% { transform: rotate(-7deg); }
  70% { transform: rotate(6deg); }
}

@media (max-width: 30rem) {
  .greeter {
    right: clamp(0.9rem, 3vw, 2rem);
    flex-direction: column-reverse;
    align-items: flex-start;
    gap: 0.5rem;
  }

  .greeter-avatar { width: 2.75rem; height: 2.75rem; }

  .greeter-bubble {
    width: 100%;
    max-width: none;
    margin-bottom: 0;
    font-size: 0.78125rem;
  }

  .greeter-bubble::before { display: none; }
}

/* ---------- 22. Utilities ---------- */
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

/* ---------- 21. 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;
    scroll-behavior: auto !important;
  }
}

@media print {
  .site-header,
  .theme-toggle,
  .hero-links,
  .to-top,
  .greeter,
  .skip-link { display: none; }

  body { background: #fff; color: #000; }
  .project, .paper, .certs li { border-color: #bbb; }
  .section { break-inside: avoid; }
}