/* ==========================================================================
   giyuubin.github.io
   Academic personal site. No build step, no external CSS.
   Layout follows isnpl.github.io: single narrow column, generous whitespace,
   quiet borders instead of shadows.
   ========================================================================== */

/* --------------------------------------------------------------------------
   1. Tokens
   Light is the default. Dark is applied two ways: explicitly via
   [data-theme="dark"] (user picked it) and implicitly via prefers-color-scheme
   (user is on "auto"). The :not() guard stops the media query from overriding
   an explicit light choice.
   -------------------------------------------------------------------------- */
:root {
  --primary: #004e96;
  --primary-hover: #0a3d78;
  --primary-subtle: rgba(0, 78, 150, 0.08);
  --on-primary: #ffffff;

  --bg: #ffffff;
  --bg-muted: #f8f9fa;
  --border: #e5e7eb;
  --border-strong: #d1d5db;
  --text: #1a1a1a;
  --text-muted: #5b6472;

  --nav-bg: rgba(255, 255, 255, 0.88);
  --nav-shadow: 0 1px 3px rgba(0, 0, 0, 0.06);

  --font-sans: 'Source Sans 3', -apple-system, BlinkMacSystemFont, 'Segoe UI',
    Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;

  --container: 900px;
  --radius: 8px;
  --section-gap: 4rem;
}

:root[data-theme='dark'] {
  --primary: #5b9bd5;
  --primary-hover: #7fb3e0;
  --primary-subtle: rgba(91, 155, 213, 0.12);
  --on-primary: #0b1220;

  --bg: #121212;
  --bg-muted: #1c1c1e;
  --border: #2e2e32;
  --border-strong: #3f3f46;
  --text: #e4e4e7;
  --text-muted: #9ca3af;

  --nav-bg: rgba(18, 18, 18, 0.88);
  --nav-shadow: 0 1px 3px rgba(0, 0, 0, 0.4);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme='light']):not([data-theme='dark']) {
    --primary: #5b9bd5;
    --primary-hover: #7fb3e0;
    --primary-subtle: rgba(91, 155, 213, 0.12);
    --on-primary: #0b1220;

    --bg: #121212;
    --bg-muted: #1c1c1e;
    --border: #2e2e32;
    --border-strong: #3f3f46;
    --text: #e4e4e7;
    --text-muted: #9ca3af;

    --nav-bg: rgba(18, 18, 18, 0.88);
    --nav-shadow: 0 1px 3px rgba(0, 0, 0, 0.4);
  }
}

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

html {
  scroll-behavior: smooth;
  /* Sticky nav would otherwise cover the top of an anchored section. */
  scroll-padding-top: 5rem;
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

h1,
h2,
h3,
h4 {
  margin: 0;
  line-height: 1.3;
  font-weight: 600;
  color: var(--text);
}

p {
  margin: 0 0 1rem;
}

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

a {
  color: var(--primary);
  text-decoration: none;
}

a:hover {
  color: var(--primary-hover);
  text-decoration: underline;
}

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

code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: var(--bg-muted);
  padding: 0.1em 0.35em;
  border-radius: 4px;
}

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

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: absolute;
  top: 0;
  left: 0;
  z-index: 200;
  padding: 0.6rem 1rem;
  background: var(--primary);
  color: var(--on-primary);
  transform: translateY(-120%);
}

.skip-link:focus {
  transform: translateY(0);
}

.container {
  width: 100%;
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 1.5rem;
}

/* --------------------------------------------------------------------------
   3. Navigation
   -------------------------------------------------------------------------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--nav-bg);
  backdrop-filter: saturate(180%) blur(12px);
  -webkit-backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid transparent;
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

.nav.is-scrolled {
  border-bottom-color: var(--border);
  box-shadow: var(--nav-shadow);
}

.nav-inner {
  display: flex;
  align-items: center;
  gap: 1rem;
  height: 4rem;
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.nav-brand {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
  color: var(--text);
  white-space: nowrap;
}

.nav-brand:hover {
  color: var(--primary);
  text-decoration: none;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  margin-left: auto;
}

.nav-links a {
  position: relative;
  padding: 0.4rem 0.7rem;
  border-radius: 6px;
  font-size: 0.95rem;
  color: var(--text-muted);
  transition: color 0.15s ease, background-color 0.15s ease;
}

.nav-links a:hover {
  color: var(--text);
  background: var(--bg-muted);
  text-decoration: none;
}

.nav-links a.is-active {
  color: var(--primary);
  font-weight: 600;
}

.nav-controls {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.theme-toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.25rem;
  height: 2.25rem;
  padding: 0;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: transparent;
  color: var(--text-muted);
  cursor: pointer;
  transition: color 0.15s ease, border-color 0.15s ease;
}

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

.theme-toggle svg {
  width: 1.1rem;
  height: 1.1rem;
  display: none;
}

/* Only the icon matching the active mode is shown. */
:root:not([data-theme]) .theme-toggle .icon-auto,
:root[data-theme='light'] .theme-toggle .icon-light,
:root[data-theme='dark'] .theme-toggle .icon-dark {
  display: block;
}

.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 4px;
  width: 2.25rem;
  height: 2.25rem;
  padding: 0;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: transparent;
  cursor: pointer;
}

.nav-toggle-bar {
  display: block;
  width: 1rem;
  height: 1.5px;
  margin: 0 auto;
  background: var(--text);
  transition: transform 0.2s ease, opacity 0.2s ease;
}

.nav-backdrop {
  position: fixed;
  inset: 0;
  z-index: 90;
  background: rgba(0, 0, 0, 0.4);
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.2s ease, visibility 0.2s ease;
}

.nav-backdrop.is-open {
  opacity: 1;
  visibility: visible;
}

/* --------------------------------------------------------------------------
   4. Hero
   -------------------------------------------------------------------------- */
.hero {
  display: flex;
  align-items: center;
  gap: 2.5rem;
  padding: 3.5rem 0 var(--section-gap);
}

.hero-avatar {
  flex: 0 0 auto;
  width: 160px;
  height: 160px;
  border-radius: 50%;
  overflow: hidden;
  background: var(--bg-muted);
  border: 1px solid var(--border);
}

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

.hero-avatar-initials {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
  height: 100%;
  font-size: 3rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  color: var(--primary);
  background: var(--primary-subtle);
}

.hero-body {
  min-width: 0;
}

.hero-name {
  font-size: 2.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: 0.25rem;
}

.hero-role {
  font-size: 1.15rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
}

.hero-orgs {
  font-size: 0.95rem;
  color: var(--text-muted);
  margin-bottom: 1.25rem;
}

.hero-orgs a {
  color: var(--text-muted);
  text-decoration: underline;
  text-decoration-color: var(--border-strong);
  text-underline-offset: 2px;
}

.hero-orgs a:hover {
  color: var(--primary);
}

.hero-social {
  display: flex;
  gap: 0.5rem;
}

.hero-social a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.4rem;
  height: 2.4rem;
  border: 1px solid var(--border);
  border-radius: 50%;
  color: var(--text-muted);
  transition: color 0.15s ease, border-color 0.15s ease,
    background-color 0.15s ease;
}

.hero-social a:hover {
  color: var(--primary);
  border-color: var(--primary);
  background: var(--primary-subtle);
  text-decoration: none;
}

.hero-social svg {
  width: 1.15rem;
  height: 1.15rem;
}

/* --------------------------------------------------------------------------
   5. Sections
   -------------------------------------------------------------------------- */
.section {
  padding-bottom: var(--section-gap);
}

.section-title {
  font-size: 1.5rem;
  padding-bottom: 0.6rem;
  margin-bottom: 1.75rem;
  border-bottom: 1px solid var(--border);
}

.section-more {
  margin-top: 1.5rem;
  font-size: 0.95rem;
}

.section-more a {
  font-weight: 600;
}

/* About ------------------------------------------------------------------- */
.about-bio p {
  margin-bottom: 1rem;
}

.about-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  margin-top: 2rem;
}

.about-heading {
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-bottom: 0.85rem;
}

.interest-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.interest-list li {
  position: relative;
  padding-left: 1.1rem;
  margin-bottom: 0.35rem;
}

.interest-list li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0.68em;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--primary);
}

.education-item {
  padding-left: 1.1rem;
  border-left: 2px solid var(--border);
  margin-bottom: 1rem;
}

.education-item:last-child {
  margin-bottom: 0;
}

.education-course {
  font-weight: 600;
}

.education-meta {
  font-size: 0.92rem;
  color: var(--text-muted);
}

/* News -------------------------------------------------------------------- */
.news-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.news-item {
  display: flex;
  gap: 1.25rem;
  padding: 0.7rem 0;
  border-bottom: 1px solid var(--border);
}

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

.news-date {
  flex: 0 0 5.5rem;
  font-size: 0.9rem;
  font-variant-numeric: tabular-nums;
  color: var(--text-muted);
  padding-top: 0.1rem;
}

.news-text {
  min-width: 0;
}

/* Publications ------------------------------------------------------------ */
.pub-group-title {
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin: 2rem 0 0.85rem;
}

.pub-group:first-child .pub-group-title {
  margin-top: 0;
}

.pub-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.pub-item {
  padding: 0.9rem 0;
  border-bottom: 1px solid var(--border);
}

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

.pub-title {
  font-size: 1.02rem;
  font-weight: 600;
  margin-bottom: 0.2rem;
}

.pub-authors,
.pub-venue {
  font-size: 0.93rem;
  color: var(--text-muted);
}

.pub-venue em {
  font-style: italic;
}

.pub-authors .is-me {
  color: var(--text);
  font-weight: 700;
}

.pub-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-top: 0.5rem;
}

.pub-link {
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  padding: 0.12rem 0.5rem;
  border: 1px solid var(--border-strong);
  border-radius: 4px;
  color: var(--text-muted);
}

.pub-link:hover {
  color: var(--primary);
  border-color: var(--primary);
  background: var(--primary-subtle);
  text-decoration: none;
}

/* Projects ---------------------------------------------------------------- */
.project-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1.25rem;
}

.card {
  display: flex;
  flex-direction: column;
  padding: 1.35rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg);
  transition: border-color 0.15s ease;
}

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

.card-title {
  font-size: 1.05rem;
  margin-bottom: 0.35rem;
}

.card-note {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 0.6rem;
}

.card-summary {
  font-size: 0.95rem;
  margin-bottom: 1rem;
}

.card-footer {
  margin-top: auto;
}

.tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin-bottom: 0.85rem;
}

.tag {
  font-size: 0.78rem;
  padding: 0.1rem 0.5rem;
  border-radius: 999px;
  background: var(--bg-muted);
  border: 1px solid var(--border);
  color: var(--text-muted);
}

.card-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.9rem;
  font-size: 0.9rem;
  font-weight: 600;
}

/* Contact ----------------------------------------------------------------- */
.contact-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.contact-list li {
  display: flex;
  gap: 0.75rem;
  margin-bottom: 0.4rem;
}

.contact-label {
  flex: 0 0 5rem;
  color: var(--text-muted);
}

/* --------------------------------------------------------------------------
   6. Subpage header
   -------------------------------------------------------------------------- */
.page-header {
  padding: 3rem 0 2rem;
}

.page-title {
  font-size: 2rem;
  letter-spacing: -0.02em;
  margin-bottom: 0.4rem;
}

.page-subtitle {
  color: var(--text-muted);
}

.back-link {
  display: inline-block;
  font-size: 0.92rem;
  color: var(--text-muted);
  margin-bottom: 1.25rem;
}

.back-link:hover {
  color: var(--primary);
  text-decoration: none;
}

.empty-state {
  padding: 2.5rem 0;
  color: var(--text-muted);
}

/* --------------------------------------------------------------------------
   7. Footer
   -------------------------------------------------------------------------- */
.footer {
  border-top: 1px solid var(--border);
  padding: 2rem 0 3rem;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.footer a {
  color: var(--text-muted);
  text-decoration: underline;
  text-decoration-color: var(--border-strong);
  text-underline-offset: 2px;
}

.footer a:hover {
  color: var(--primary);
}

/* --------------------------------------------------------------------------
   8. Responsive
   -------------------------------------------------------------------------- */
@media (max-width: 720px) {
  :root {
    --section-gap: 3rem;
  }

  .nav-toggle {
    display: flex;
    order: 3;
  }

  .nav-controls {
    margin-left: auto;
    order: 2;
  }

  /* Off-canvas panel. Hidden from the a11y tree and tab order when closed
     via `visibility`, which `transform` alone would not do. */
  .nav-links {
    position: fixed;
    top: 4rem;
    left: 0;
    right: 0;
    z-index: 95;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    margin-left: 0;
    padding: 0.5rem 1.5rem 1rem;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.12);
    transform: translateY(-8px);
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.2s ease, transform 0.2s ease, visibility 0.2s ease;
  }

  .nav-links.is-open {
    transform: translateY(0);
    opacity: 1;
    visibility: visible;
    /* Opening has to flip visibility synchronously. nav.js focuses the first
       link the instant `.is-open` is added, and focus() is silently a no-op
       while the panel is still `visibility: hidden` — the delay above left the
       menu open with focus stranded on the toggle. Closing still uses the 0.2s
       from the rule above, so the panel stays focusable and in the a11y tree
       until the fade has finished. */
    transition: opacity 0.2s ease, transform 0.2s ease, visibility 0s;
  }

  .nav-links a {
    padding: 0.7rem 0.5rem;
    font-size: 1rem;
    border-radius: 0;
    border-bottom: 1px solid var(--border);
  }

  .nav-links a:last-child {
    border-bottom: none;
  }

  .hero {
    flex-direction: column;
    align-items: center;
    text-align: center;
    gap: 1.5rem;
    padding-top: 2.5rem;
  }

  .hero-avatar {
    width: 128px;
    height: 128px;
  }

  .hero-name {
    font-size: 2rem;
  }

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

  .about-grid,
  .project-grid {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }

  .news-item {
    flex-direction: column;
    gap: 0.15rem;
  }

  .news-date {
    flex: none;
    font-size: 0.85rem;
  }

  .contact-list li {
    flex-direction: column;
    gap: 0;
    margin-bottom: 0.75rem;
  }

  .contact-label {
    flex: none;
    font-size: 0.85rem;
  }
}

/* --------------------------------------------------------------------------
   9. 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,
  .nav-backdrop,
  .skip-link,
  .section-more {
    display: none !important;
  }

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

  a {
    color: #000;
    text-decoration: underline;
  }
}