/* ============================================================
   MONOGRAPH — Academic Personal Website
   Swiss/Clean Precision Design System
   Zhibo Eric Sun
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=DM+Sans:ital,opsz,wght@0,9..40,300;0,9..40,400;0,9..40,500;0,9..40,600;0,9..40,700;1,9..40,400&family=Instrument+Serif:ital@0;1&display=swap');

/* ─── Custom Properties ─────────────────────────────────── */
:root {
  /* Palette */
  --color-bg: #ffffff;
  --color-sidebar: #14283e;
  --color-sidebar-text: #dce4ec;
  --color-sidebar-muted: #8fa3b8;
  --color-accent: #2563eb;
  --color-accent-hover: #1d4ed8;
  --color-text: #111827;
  --color-text-secondary: #374151;
  --color-rule: #e5e7eb;
  --color-rule-light: #f3f4f6;

  /* Typography */
  --font-display: 'Instrument Serif', Georgia, serif;
  --font-body: 'DM Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;

  /* Spacing scale (4px base) */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2.5rem;
  --space-2xl: 4rem;
  --space-3xl: 6rem;

  /* Layout */
  --sidebar-width: clamp(300px, 20vw, 380px);
  --content-max-width: 54rem;
  --border-radius-sm: 2px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;
}

/* ─── Reset & Base ──────────────────────────────────────── */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-weight: 400;
  font-size: 1rem;
  line-height: 1.7;
  color: var(--color-text);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

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

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

ul, ol {
  list-style: none;
}

/* ─── Skip Link ─────────────────────────────────────────── */
.skip-link {
  position: absolute;
  top: -100%;
  left: 1rem;
  z-index: 9999;
  padding: 0.75rem 1.5rem;
  background: var(--color-accent);
  color: #fff;
  font-size: 0.875rem;
  font-weight: 500;
  border-radius: var(--border-radius-sm);
  transition: top var(--transition-fast);
}

.skip-link:focus {
  top: 1rem;
  color: #fff;
}

/* ─── Screen Reader Only ────────────────────────────────── */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* ─── Site Layout ───────────────────────────────────────── */
.site-layout {
  display: flex;
  min-height: 100vh;
}

/* ─── Sidebar ───────────────────────────────────────────── */
.sidebar {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 100;
  width: var(--sidebar-width);
  height: 100vh;
  background-color: var(--color-sidebar);
  color: var(--color-sidebar-text);
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  padding: var(--space-2xl) var(--space-xl) var(--space-lg);
}

.sidebar::before {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(
    180deg,
    rgba(255, 255, 255, 0.03) 0%,
    transparent 40%,
    transparent 70%,
    rgba(0, 0, 0, 0.15) 100%
  );
  pointer-events: none;
}

/* Sidebar Profile */
.sidebar-profile {
  position: relative;
  z-index: 1;
  text-align: center;
  margin-bottom: var(--space-xl);
}

.sidebar-photo {
  width: 160px;
  height: 160px;
  border-radius: 50%;
  object-fit: cover;
  border: 2px solid rgba(255, 255, 255, 0.12);
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.25);
  margin: 0 auto var(--space-xl);
  display: block;
}

.sidebar-name {
  font-family: var(--font-display);
  font-size: 1.65rem;
  font-weight: 400;
  color: #ffffff;
  letter-spacing: -0.01em;
  line-height: 1.25;
  margin-bottom: 0.4rem;
}

.sidebar-title {
  font-size: 0.938rem;
  font-weight: 400;
  color: var(--color-sidebar-muted);
  line-height: 1.6;
  letter-spacing: 0.005em;
}

.sidebar-title a {
  color: var(--color-sidebar-text);
  transition: color var(--transition-fast);
  text-decoration: none;
}

.sidebar-title a:hover {
  color: #ffffff;
}

/* Sidebar Navigation */
.sidebar-nav {
  position: relative;
  z-index: 1;
  margin-bottom: auto;
  padding: var(--space-lg) 0;
  border-top: 1px solid rgba(255, 255, 255, 0.08);
}

.sidebar-nav ul {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.sidebar-nav a {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  padding: 0.7rem var(--space-md);
  color: var(--color-sidebar-muted);
  font-size: 1rem;
  font-weight: 400;
  letter-spacing: 0.01em;
  border-left: 2px solid transparent;
  border-radius: 0;
  transition:
    color var(--transition-fast),
    border-color var(--transition-fast),
    background-color var(--transition-fast);
}

.sidebar-nav a i {
  font-size: 0.95rem;
  width: 1.25rem;
  text-align: center;
  opacity: 0.6;
  transition: opacity var(--transition-fast);
}

.sidebar-nav a:hover i,
.sidebar-nav a.active i {
  opacity: 1;
}

.sidebar-nav a:hover {
  color: #ffffff;
  background-color: rgba(255, 255, 255, 0.04);
}

.sidebar-nav a.active {
  color: #ffffff;
  border-left-color: var(--color-accent);
  background-color: rgba(37, 99, 235, 0.1);
  font-weight: 500;
}

/* Sidebar Social */
.sidebar-social {
  position: relative;
  z-index: 1;
  display: flex;
  justify-content: center;
  gap: 0.75rem;
  padding-top: var(--space-xl);
  border-top: 1px solid rgba(255, 255, 255, 0.08);
}

.sidebar-social a {
  color: var(--color-sidebar-muted);
  font-size: 1.2rem;
  transition: all var(--transition-fast);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.5rem;
  height: 2.5rem;
  border-radius: var(--border-radius-sm);
}

.sidebar-social a:hover {
  color: #ffffff;
  background: rgba(255, 255, 255, 0.06);
}

/* ─── Main Content ──────────────────────────────────────── */
.main-content {
  margin-left: var(--sidebar-width);
  flex: 1;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  padding: var(--space-3xl) clamp(2.5rem, 6vw, 8rem) var(--space-2xl) clamp(3rem, 8vw, 10rem);
}

.content-area {
  width: 100%;
  max-width: var(--content-max-width);
}

/* ─── Mobile Header ─────────────────────────────────────── */
.mobile-header {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 90;
  height: 56px;
  background: var(--color-sidebar);
  color: #ffffff;
  align-items: center;
  justify-content: space-between;
  padding: 0 var(--space-md);
}

.mobile-header .sidebar-name {
  font-family: var(--font-display);
  font-size: 1.1rem;
  margin-bottom: 0;
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
  color: #ffffff;
  -webkit-tap-highlight-color: transparent;
}

.hamburger {
  display: block;
  width: 20px;
  height: 2px;
  background: #ffffff;
  position: relative;
  transition: background var(--transition-fast);
}

.hamburger::before,
.hamburger::after {
  content: '';
  position: absolute;
  left: 0;
  width: 20px;
  height: 2px;
  background: #ffffff;
  transition: transform var(--transition-base);
}

.hamburger::before {
  top: -6px;
}

.hamburger::after {
  top: 6px;
}

/* Hamburger active state */
.sidebar.open ~ .mobile-header .hamburger,
.nav-toggle[aria-expanded="true"] .hamburger {
  background: transparent;
}

.sidebar.open ~ .mobile-header .hamburger::before,
.nav-toggle[aria-expanded="true"] .hamburger::before {
  top: 0;
  transform: rotate(45deg);
}

.sidebar.open ~ .mobile-header .hamburger::after,
.nav-toggle[aria-expanded="true"] .hamburger::after {
  top: 0;
  transform: rotate(-45deg);
}

/* Sidebar Overlay */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 95;
  background: rgba(0, 0, 0, 0.5);
  opacity: 0;
  transition: opacity var(--transition-base);
}

.sidebar-overlay.active {
  opacity: 1;
}

/* ─── Page Header ───────────────────────────────────────── */
.page-header {
  margin-bottom: var(--space-2xl);
  padding-bottom: var(--space-lg);
  border-bottom: 1px solid var(--color-rule);
}

.page-header h1 {
  font-family: var(--font-display);
  font-size: clamp(2rem, 4vw, 2.75rem);
  font-weight: 400;
  color: var(--color-text);
  letter-spacing: -0.02em;
  line-height: 1.2;
}

/* ─── Section Title ─────────────────────────────────────── */
.section-title {
  font-family: var(--font-display);
  font-size: clamp(1.5rem, 3vw, 2rem);
  font-weight: 400;
  color: var(--color-text);
  letter-spacing: -0.015em;
  line-height: 1.25;
  margin-bottom: var(--space-lg);
  padding-bottom: var(--space-sm);
  border-bottom: 1px solid var(--color-rule);
}

/* ─── Home Content ──────────────────────────────────────── */
.home-content {
  font-size: 1.1rem;
  line-height: 1.85;
  color: var(--color-text);
  max-width: 62ch;
}

.home-content p {
  margin-bottom: var(--space-lg);
}

.home-content p:last-child {
  margin-bottom: 0;
}

.home-content strong {
  color: var(--color-text);
  font-weight: 600;
}

/* ─── Content Section ───────────────────────────────────── */
.content-section {
  margin-bottom: var(--space-2xl);
}

.content-section h3 {
  font-family: var(--font-display);
  font-size: 1.35rem;
  font-weight: 400;
  color: var(--color-text);
  letter-spacing: -0.01em;
  margin-bottom: var(--space-md);
}

.content-section p {
  margin-bottom: var(--space-md);
  color: var(--color-text-secondary);
  line-height: 1.75;
}

.content-section ul {
  list-style: none;
}

.content-section li {
  padding: 0.5rem 0;
  border-bottom: 1px solid var(--color-rule-light);
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  line-height: 1.65;
}

.content-section li:last-child {
  border-bottom: none;
}

/* ─── Publication List ──────────────────────────────────── */
.pub-list {
  display: flex;
  flex-direction: column;
}

/* ─── Publication Card ──────────────────────────────────── */
.pub-card {
  padding: var(--space-lg) 0;
  border-bottom: 1px solid var(--color-rule);
}

.pub-card:first-child {
  padding-top: 0;
}

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

.pub-title {
  font-family: var(--font-body);
  font-size: 1.08rem;
  font-weight: 600;
  color: var(--color-text);
  line-height: 1.5;
  margin-bottom: var(--space-sm);
}

.pub-title a {
  color: var(--color-text);
  transition: color var(--transition-fast);
}

.pub-title a:hover {
  color: var(--color-accent);
}

.pub-authors {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: var(--space-sm);
}

.pub-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-sm);
  margin-bottom: var(--space-sm);
}

.venue-badge {
  display: inline-block;
  padding: 0.15rem 0.55rem;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  color: var(--color-accent);
  border: 1px solid var(--color-accent);
  border-radius: var(--border-radius-sm);
  line-height: 1.6;
}

.award-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.15rem 0.55rem;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  color: #b45309;
  background-color: #fffbeb;
  border: 1px solid #fbbf24;
  border-radius: var(--border-radius-sm);
  line-height: 1.6;
}

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

.pub-link {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.2rem 0;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--color-accent);
  border-bottom: 1px solid transparent;
  transition:
    color var(--transition-fast),
    border-color var(--transition-fast);
}

.pub-link:hover {
  color: var(--color-accent-hover);
  border-bottom-color: var(--color-accent-hover);
}

/* ─── Recruit Card ──────────────────────────────────────── */
.recruit-card {
  padding: var(--space-lg);
  border: 1px solid var(--color-accent);
  border-radius: var(--border-radius-sm);
  background: rgba(37, 99, 235, 0.03);
  margin-bottom: var(--space-xl);
}

.recruit-card h3 {
  font-family: var(--font-display);
  font-size: 1.2rem;
  font-weight: 400;
  color: var(--color-text);
  margin-bottom: var(--space-sm);
}

.recruit-card p {
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
}

/* ─── Student Card ──────────────────────────────────────── */
.student-card {
  padding: var(--space-md) 0;
  border-bottom: 1px solid var(--color-rule);
}

.student-card:last-child {
  border-bottom: none;
}

.student-info {
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
}

.student-info h3 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-text);
}

.student-info p {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
}

/* ─── Footer ────────────────────────────────────────────── */
.site-footer {
  width: 100%;
  max-width: var(--content-max-width);
  margin-top: auto;
  padding-top: var(--space-2xl);
  border-top: 1px solid var(--color-rule);
  text-align: center;
  font-size: 0.8rem;
  color: var(--color-text-secondary);
  letter-spacing: 0.01em;
  line-height: 1.6;
}

.site-footer p {
  margin-bottom: var(--space-xs);
}

/* ─── Fade-In Animation ─────────────────────────────────── */
.fade-in {
  opacity: 0;
  transform: translateY(12px);
  transition:
    opacity var(--transition-slow),
    transform var(--transition-slow);
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Staggered publication cards */
.pub-card.fade-in:nth-child(1) { transition-delay: 0ms; }
.pub-card.fade-in:nth-child(2) { transition-delay: 60ms; }
.pub-card.fade-in:nth-child(3) { transition-delay: 120ms; }
.pub-card.fade-in:nth-child(4) { transition-delay: 180ms; }
.pub-card.fade-in:nth-child(5) { transition-delay: 240ms; }
.pub-card.fade-in:nth-child(6) { transition-delay: 300ms; }
.pub-card.fade-in:nth-child(7) { transition-delay: 360ms; }
.pub-card.fade-in:nth-child(8) { transition-delay: 420ms; }
.pub-card.fade-in:nth-child(9) { transition-delay: 480ms; }
.pub-card.fade-in:nth-child(10) { transition-delay: 540ms; }

/* ─── Utility Classes ───────────────────────────────────── */
.mt-lg {
  margin-top: var(--space-lg);
}

.mt-xl {
  margin-top: var(--space-xl);
}

.mb-lg {
  margin-bottom: var(--space-lg);
}

/* ─── Reduced Motion ────────────────────────────────────── */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  .fade-in {
    opacity: 1;
    transform: none;
    transition: none;
  }
}

/* ─── Responsive: Tablet / Mobile (< 768px) ────────────── */
@media (max-width: 768px) {
  .mobile-header {
    display: flex;
  }

  .nav-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
  }

  .sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: 280px;
    height: 100vh;
    transform: translateX(-100%);
    transition: transform var(--transition-base);
    z-index: 100;
    padding-top: var(--space-2xl);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .sidebar-overlay {
    display: block;
    pointer-events: none;
  }

  .sidebar-overlay.active {
    pointer-events: auto;
  }

  .main-content {
    margin-left: 0;
    padding: calc(56px + var(--space-xl)) var(--space-md) var(--space-xl);
    align-items: stretch;
  }

  .page-header h1 {
    font-size: 1.75rem;
  }

  .section-title {
    font-size: 1.35rem;
  }

  .pub-card {
    padding: var(--space-md) 0;
  }

  .pub-title {
    font-size: 1rem;
  }

  .pub-meta {
    gap: var(--space-xs);
  }

  .recruit-card {
    padding: var(--space-md);
  }

  .site-footer {
    padding-top: var(--space-xl);
  }
}

/* ─── Fine-tuning for very small screens ────────────────── */
@media (max-width: 480px) {
  .main-content {
    padding-left: var(--space-md);
    padding-right: var(--space-md);
  }

  .sidebar-photo {
    width: 100px;
    height: 100px;
  }

  .pub-links {
    gap: var(--space-xs);
  }
}