/* ---------- Design tokens ---------- */
:root {
  --color-bg: #ffffff;
  --color-bg-alt: #f5f5f7;
  --color-text: #1d1d1f;
  --color-text-muted: #6e6e73;
  --color-border: #e5e5ea;
  --color-accent: #0a66ff;
  --color-accent-hover: #0050d6;

  --font-sans: "Inter", "Noto Sans KR", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;

  --max-width: 920px;
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 40px;
  --space-5: 64px;
  --space-6: 96px;

  --radius: 12px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #000000;
    --color-bg-alt: #1c1c1e;
    --color-text: #f5f5f7;
    --color-text-muted: #98989d;
    --color-border: #2c2c2e;
    --color-accent: #4d9fff;
    --color-accent-hover: #7ab8ff;
  }
}

/* ---------- Reset ---------- */
* { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }
ul { list-style: none; }

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-3);
}

/* ---------- Scroll reveal ---------- */
[data-reveal] {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.7s ease, transform 0.7s ease;
}

[data-reveal].is-visible {
  opacity: 1;
  transform: translateY(0);
}

/* ---------- Kinetic hero typography ---------- */
[data-kinetic] {
  overflow: hidden;
}

[data-kinetic] .char {
  display: inline-block;
  opacity: 0;
  transform: translateY(0.6em);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

[data-kinetic] .char.is-in {
  opacity: 1;
  transform: translateY(0);
}

.hero-inner {
  transition: transform 0.1s linear, opacity 0.1s linear;
  will-change: transform, opacity;
}

@media (prefers-reduced-motion: reduce) {
  [data-reveal] {
    opacity: 1;
    transform: none;
    transition: none;
  }
  [data-kinetic] .char {
    opacity: 1;
    transform: none;
    transition: none;
  }
  .hero-inner {
    transition: none;
  }
  html {
    scroll-behavior: auto;
  }
}

/* ---------- Header / Nav ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: color-mix(in srgb, var(--color-bg) 85%, transparent);
  backdrop-filter: saturate(180%) blur(20px);
  border-bottom: 1px solid var(--color-border);
}

.nav {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--space-2) var(--space-3);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-weight: 600;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
}

.nav-links {
  display: flex;
  gap: var(--space-4);
}

.nav-links a {
  font-size: 0.95rem;
  color: var(--color-text-muted);
  transition: color 0.15s ease;
}

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

.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 5px;
  width: 44px;
  height: 44px;
  background: none;
  border: none;
  cursor: pointer;
}

.nav-toggle span {
  width: 20px;
}

.nav-toggle span {
  display: block;
  height: 2px;
  background: var(--color-text);
  border-radius: 2px;
}

/* ---------- Hero ---------- */
.hero {
  padding: var(--space-6) 0 var(--space-5);
}

.hero-inner {
  text-align: center;
  width: 100%;
}

.eyebrow {
  color: var(--color-text-muted);
  font-size: 0.9rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  margin-bottom: var(--space-2);
}

.hero h1 {
  font-size: clamp(2.5rem, 6vw, 3.5rem);
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: var(--space-2);
}

.hero-tagline {
  color: var(--color-text-muted);
  font-size: 1.15rem;
  max-width: 560px;
  margin: 0 auto var(--space-4);
}

.social-links {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--space-2);
  justify-content: center;
}

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

.icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  border: 1px solid var(--color-border);
  color: var(--color-text);
  transition: background 0.15s ease, border-color 0.15s ease, transform 0.15s ease;
}

.icon-btn svg {
  width: 20px;
  height: 20px;
}

.icon-btn:hover {
  background: var(--color-bg-alt);
  border-color: var(--color-text-muted);
  transform: translateY(-1px);
}

.btn {
  display: inline-block;
  padding: 10px 20px;
  border-radius: 999px;
  font-size: 0.95rem;
  font-weight: 500;
  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease;
}

.btn-primary {
  background: var(--color-accent);
  color: #fff;
}

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

.btn-ghost {
  border: 1px solid var(--color-border);
  color: var(--color-text);
}

.btn-ghost:hover { border-color: var(--color-text-muted); }

/* ---------- Sections ---------- */
.section {
  padding: var(--space-6) 0;
}

.section-alt {
  background: var(--color-bg-alt);
}

@media (prefers-color-scheme: dark) {
  .section-dark {
    background: var(--color-bg);
    color: var(--color-text);
  }
}

.section-title {
  font-size: 1.8rem;
  font-weight: 700;
  letter-spacing: -0.01em;
  margin-bottom: var(--space-4);
}

/* ---------- About ---------- */
.about-grid {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: var(--space-4);
  align-items: start;
}

.about-photo {
  width: 200px;
  height: 200px;
  border-radius: 50%;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  overflow: hidden;
}

.about-photo img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  object-position: center 15%;
}

.about-text p {
  margin-bottom: var(--space-2);
  color: var(--color-text-muted);
}

.hero-tagline a,
.about-text a {
  color: var(--color-accent);
  text-decoration: underline;
  text-underline-offset: 2px;
}

.hero-tagline a:hover,
.about-text a:hover {
  color: var(--color-accent-hover);
}

.interest-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
  margin-top: var(--space-3);
}

.interest-tags li {
  padding: 6px 14px;
  border-radius: 999px;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

/* ---------- Publications ---------- */
.pub-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.pub-item {
  display: grid;
  grid-template-columns: 80px 1fr;
  gap: var(--space-3);
  padding-bottom: var(--space-4);
  border-bottom: 1px solid var(--color-border);
}

.pub-item:last-child {
  border-bottom: none;
  padding-bottom: 0;
}

.pub-year {
  font-weight: 600;
  color: var(--color-text-muted);
}

.pub-title {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: var(--space-1);
}

.pub-authors, .pub-venue {
  color: var(--color-text-muted);
  font-size: 0.95rem;
  margin-bottom: 4px;
}

.pub-links {
  display: flex;
  gap: var(--space-2);
  margin-top: var(--space-1);
}

.pub-links a {
  font-size: 0.85rem;
  color: var(--color-accent);
  font-weight: 500;
}

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

/* ---------- CV ---------- */
.cv-block {
  margin-bottom: var(--space-4);
}

.cv-block-title {
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-2);
}

.cv-entry {
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: var(--space-3);
  padding: var(--space-2) 0;
  border-bottom: 1px solid var(--color-border);
}

.cv-entry:last-child { border-bottom: none; }

.cv-entry-time {
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

.cv-entry-title { font-weight: 600; }

.cv-entry-sub {
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

/* ---------- Contact ---------- */
.contact-inner {
  text-align: center;
}

.contact-inner p {
  color: var(--color-text-muted);
  margin-bottom: var(--space-3);
}

/* ---------- Footer ---------- */
.site-footer {
  padding: var(--space-4) 0;
  border-top: 1px solid var(--color-border);
}

.site-footer p {
  color: var(--color-text-muted);
  font-size: 0.85rem;
  text-align: center;
}

/* ---------- Responsive ---------- */
@media (max-width: 720px) {
  .nav-links {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--color-bg);
    border-bottom: 1px solid var(--color-border);
    flex-direction: column;
    padding: var(--space-2) var(--space-3);
    gap: var(--space-2);
    display: none;
  }

  .nav-links.open { display: flex; }

  .nav-toggle { display: flex; }

  .about-grid {
    grid-template-columns: 1fr;
    justify-items: center;
    text-align: center;
  }

  .pub-item, .cv-entry {
    grid-template-columns: 1fr;
    gap: var(--space-1);
  }

  .hero {
    min-height: 100vh;
    min-height: 100dvh;
    display: flex;
    align-items: center;
    padding: var(--space-5) 0 var(--space-4);
  }

  .section {
    padding: var(--space-5) 0;
  }

  .hero-tagline {
    font-size: 1rem;
  }
}

@media (max-width: 400px) {
  .container {
    padding: 0 var(--space-2);
  }

  .about-photo {
    width: 150px;
    height: 150px;
  }

  .social-links {
    gap: var(--space-1);
  }

  .icon-btn {
    width: 40px;
    height: 40px;
  }
}