/* ============================================================
   KNOWLEDGE CIRCUIT — DESIGN SYSTEM & STYLES
   ============================================================ */

:root {
  /* Core Color Palette */
  --charcoal: #15171D;
  --charcoal-light: #1E2129;
  --charcoal-card: #222631;
  --violet: #7667F5;
  --violet-hover: #6150E6;
  --violet-subtle: #F0EDFF;
  --violet-glow: rgba(118, 103, 245, 0.25);
  --yellow: #F2C94C;
  --yellow-hover: #E3B93B;
  --yellow-subtle: #FFF9E6;
  --ice: #B9E8F5;
  --ice-subtle: #EDFAFD;
  --lavender: #E9E5FF;
  --off-white: #F8F8F5;
  --white: #FFFFFF;
  --text: #252833;
  --text-light: #484D5E;
  --muted: #6D7280;
  --border: #DDDDE5;
  --border-subtle: #E8E8EE;
  --border-dark: #2D3240;

  /* Typography */
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;

  /* Geometry & Layout */
  --radius-xs: 4px;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-xl: 28px;
  --radius-full: 9999px;
  --radius: 14px;

  /* Shadows */
  --shadow-sm: 0 2px 6px rgba(21, 23, 29, 0.04);
  --shadow-md: 0 8px 24px rgba(21, 23, 29, 0.08);
  --shadow-lg: 0 16px 40px rgba(21, 23, 29, 0.12);
  --shadow: 0 8px 24px rgba(21, 23, 29, 0.08);

  /* Transitions */
  --transition-fast: 0.18s cubic-bezier(0.16, 1, 0.3, 1);
  --transition: 0.28s cubic-bezier(0.16, 1, 0.3, 1);
  --transition-smooth: 0.45s cubic-bezier(0.16, 1, 0.3, 1);

  /* Container */
  --container-max: 1200px;
  --header-height: 72px;
}

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

html {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--text);
  background-color: var(--off-white);
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-height) + 16px);
  -webkit-text-size-adjust: 100%;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  color: var(--text);
  background-color: var(--off-white);
  overflow-x: hidden;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

/* Accessibility Focus States */
:focus-visible {
  outline: 2px solid var(--violet);
  outline-offset: 3px;
  border-radius: var(--radius-xs);
}

/* Skip Link */
.skip-link {
  position: absolute;
  top: -60px;
  left: 20px;
  background: var(--charcoal);
  color: var(--yellow);
  padding: 10px 18px;
  border-radius: var(--radius-sm);
  font-weight: 700;
  font-size: 0.9rem;
  z-index: 9999;
  text-decoration: none;
  transition: top var(--transition-fast);
  box-shadow: var(--shadow-md);
}

.skip-link:focus {
  top: 16px;
}

/* Global Container */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-left: auto;
  margin-right: auto;
  padding-left: 24px;
  padding-right: 24px;
}

/* Section Header Structure */
.section-header {
  margin-bottom: 48px;
  max-width: 780px;
}

.section-header.centered {
  margin-left: auto;
  margin-right: auto;
  text-align: center;
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--violet);
  background-color: var(--lavender);
  padding: 4px 12px;
  border-radius: var(--radius-full);
  margin-bottom: 16px;
}

.eyebrow.dark-mode {
  background-color: rgba(118, 103, 245, 0.2);
  color: var(--ice);
  border: 1px solid rgba(185, 232, 245, 0.25);
}

.section-title {
  font-size: clamp(1.85rem, 3.2vw, 2.5rem);
  font-weight: 800;
  line-height: 1.22;
  color: var(--charcoal);
  letter-spacing: -0.02em;
  margin-bottom: 16px;
}

.section-title.dark-mode {
  color: var(--off-white);
}

.section-desc {
  font-size: 1.1rem;
  line-height: 1.65;
  color: var(--text-light);
}

.section-desc.dark-mode {
  color: #C0C3CE;
}

/* ============================================================
   STICKY HEADER & NAVIGATION
   ============================================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 1000;
  height: var(--header-height);
  background-color: rgba(248, 248, 245, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  transition: background-color var(--transition), box-shadow var(--transition);
}

.site-header.is-scrolled {
  box-shadow: var(--shadow-sm);
  background-color: rgba(248, 248, 245, 0.97);
}

.header-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.brand-link {
  display: flex;
  align-items: center;
  text-decoration: none;
  transition: opacity var(--transition-fast);
}

.brand-link:hover {
  opacity: 0.88;
}

.brand-logo-img {
  height: 40px;
  width: auto;
  display: block;
}

.nav-desktop {
  display: flex;
  align-items: center;
  gap: 8px;
}

.nav-desktop-list {
  display: flex;
  align-items: center;
  list-style: none;
  gap: 6px;
}

.nav-link {
  position: relative;
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-light);
  text-decoration: none;
  padding: 8px 16px;
  border-radius: var(--radius-full);
  transition: color var(--transition-fast), background-color var(--transition-fast);
}

.nav-link:hover {
  color: var(--violet);
  background-color: var(--lavender);
}

.nav-link.active {
  color: var(--violet);
  background-color: var(--lavender);
}

.nav-link.active::after {
  content: "";
  position: absolute;
  bottom: 4px;
  left: 50%;
  transform: translateX(-50%);
  width: 14px;
  height: 2px;
  background-color: var(--violet);
  border-radius: var(--radius-full);
}

/* Mobile Menu Toggle Button */
.mobile-toggle {
  display: none;
  align-items: center;
  gap: 8px;
  padding: 8px 14px;
  font-family: var(--font-sans);
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--charcoal);
  background-color: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius-full);
  cursor: pointer;
  transition: background-color var(--transition-fast), border-color var(--transition-fast);
}

.mobile-toggle:hover {
  background-color: var(--lavender);
  border-color: var(--violet);
}

.mobile-toggle-icon {
  width: 18px;
  height: 14px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  position: relative;
}

.mobile-toggle-icon span {
  display: block;
  height: 2px;
  width: 100%;
  background-color: var(--charcoal);
  border-radius: 2px;
  transition: transform var(--transition-fast), opacity var(--transition-fast);
}

.mobile-toggle[aria-expanded="true"] .mobile-toggle-icon span:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.mobile-toggle[aria-expanded="true"] .mobile-toggle-icon span:nth-child(2) {
  opacity: 0;
}

.mobile-toggle[aria-expanded="true"] .mobile-toggle-icon span:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

/* Mobile Nav Drawer */
.nav-mobile {
  display: none;
  position: fixed;
  top: var(--header-height);
  left: 0;
  right: 0;
  background-color: var(--white);
  border-bottom: 1px solid var(--border);
  box-shadow: var(--shadow-lg);
  padding: 20px 24px 28px;
  transform: translateY(-10px);
  opacity: 0;
  pointer-events: none;
  transition: transform var(--transition), opacity var(--transition);
  z-index: 999;
}

.nav-mobile.is-open {
  transform: translateY(0);
  opacity: 1;
  pointer-events: auto;
}

.nav-mobile-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.nav-mobile-link {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text);
  text-decoration: none;
  border-radius: var(--radius-md);
  background-color: var(--off-white);
  transition: background-color var(--transition-fast), color var(--transition-fast);
}

.nav-mobile-link:hover, .nav-mobile-link.active {
  background-color: var(--lavender);
  color: var(--violet);
}

/* ============================================================
   BUTTONS
   ============================================================ */
.btn-group {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 14px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  font-family: var(--font-sans);
  font-size: 0.98rem;
  font-weight: 700;
  padding: 13px 26px;
  border-radius: var(--radius-full);
  text-decoration: none;
  cursor: pointer;
  transition: transform var(--transition-fast), background-color var(--transition-fast), box-shadow var(--transition-fast), border-color var(--transition-fast), color var(--transition-fast);
  border: 1.5px solid transparent;
}

.btn:active {
  transform: scale(0.98);
}

.btn-primary {
  background-color: var(--violet);
  color: var(--white);
  box-shadow: 0 4px 14px var(--violet-glow);
}

.btn-primary:hover {
  background-color: var(--violet-hover);
  box-shadow: 0 6px 20px rgba(118, 103, 245, 0.4);
  transform: translateY(-2px);
}

.btn-secondary {
  background-color: var(--white);
  color: var(--charcoal);
  border-color: var(--border);
}

.btn-secondary:hover {
  background-color: var(--lavender);
  border-color: var(--violet);
  color: var(--violet);
  transform: translateY(-2px);
}

/* ============================================================
   HERO SECTION
   ============================================================ */
.hero-section {
  padding-top: 60px;
  padding-bottom: 80px;
  position: relative;
  overflow: hidden;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.9fr;
  align-items: center;
  gap: 48px;
}

.hero-content {
  position: relative;
  z-index: 2;
}

.hero-title {
  font-size: clamp(2.3rem, 4.4vw, 3.6rem);
  font-weight: 800;
  line-height: 1.15;
  letter-spacing: -0.03em;
  color: var(--charcoal);
  margin-bottom: 22px;
}

.hero-highlight {
  position: relative;
  display: inline;
  color: var(--violet);
  text-decoration: none;
  background: linear-gradient(120deg, rgba(118, 103, 245, 0.12) 0%, rgba(185, 232, 245, 0.28) 100%);
  padding: 0 6px;
  border-radius: var(--radius-xs);
  border-bottom: 2.5px solid var(--violet);
}

.hero-desc {
  font-size: 1.2rem;
  line-height: 1.65;
  color: var(--text-light);
  margin-bottom: 34px;
  max-width: 580px;
}

/* Hero Right Visual Stage */
.hero-visual-stage {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 36px 20px;
}

.hero-circuit-card {
  position: relative;
  width: 100%;
  max-width: 420px;
  aspect-ratio: 1 / 1;
  background: radial-gradient(circle at center, #1E222D 0%, #15171D 100%);
  border: 1.5px solid var(--border-dark);
  border-radius: var(--radius-xl);
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-lg), 0 0 35px rgba(118, 103, 245, 0.18);
  overflow: visible;
}

.hero-mark-center {
  width: 150px;
  height: 150px;
  z-index: 2;
  filter: drop-shadow(0 8px 24px rgba(0, 0, 0, 0.4));
  transition: transform var(--transition-smooth);
}

.hero-circuit-card:hover .hero-mark-center {
  transform: scale(1.04);
}

/* Decorative Background Grid in Card */
.hero-card-grid {
  position: absolute;
  inset: 12px;
  border: 1px dashed rgba(185, 232, 245, 0.14);
  border-radius: var(--radius-lg);
  pointer-events: none;
}

/* Floating Badges */
.floating-badge {
  position: absolute;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 16px;
  border-radius: var(--radius-full);
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  background-color: var(--white);
  color: var(--charcoal);
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.18);
  border: 1.5px solid var(--border);
  z-index: 4;
  animation: floatSlow 6s ease-in-out infinite alternate;
  white-space: nowrap;
}

.floating-badge::before {
  content: "";
  display: inline-block;
  width: 8px;
  height: 8px;
  border-radius: 50%;
}

.badge-structure {
  top: -12px;
  left: -8px;
  border-color: var(--violet);
  animation-delay: 0s;
}
.badge-structure::before {
  background-color: var(--violet);
}

.badge-signal {
  top: 18px;
  right: -16px;
  border-color: var(--yellow);
  animation-delay: 1.5s;
}
.badge-signal::before {
  background-color: var(--yellow);
}

.badge-interaction {
  bottom: 24px;
  left: -20px;
  border-color: var(--ice);
  animation-delay: 3s;
}
.badge-interaction::before {
  background-color: #5BC3DB;
}

.badge-practice {
  bottom: -12px;
  right: 12px;
  border-color: var(--violet);
  animation-delay: 4.5s;
}
.badge-practice::before {
  background-color: var(--violet);
}

@keyframes floatSlow {
  0% { transform: translateY(0px); }
  100% { transform: translateY(-8px); }
}

/* ============================================================
   PRINCIPLES STRIP
   ============================================================ */
.principles-strip {
  background-color: var(--charcoal);
  color: var(--off-white);
  padding: 22px 0;
  border-top: 1px solid var(--border-dark);
  border-bottom: 1px solid var(--border-dark);
}

.principles-flow {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 16px 22px;
  text-align: center;
}

.principle-item {
  font-family: var(--font-sans);
  font-size: 1.05rem;
  font-weight: 700;
  letter-spacing: -0.01em;
  color: var(--off-white);
}

.principle-separator {
  color: var(--yellow);
  font-size: 1.1rem;
  line-height: 1;
  user-select: none;
}

/* ============================================================
   LEARNING FIELDS SECTION (#fields)
   ============================================================ */
.fields-section {
  padding: 96px 0;
}

.fields-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;
}

.field-card {
  background-color: var(--white);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 32px 26px;
  display: flex;
  flex-direction: column;
  transition: transform var(--transition), border-color var(--transition), box-shadow var(--transition);
  position: relative;
  overflow: hidden;
}

.field-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--border);
  transition: background var(--transition);
}

.field-card:hover {
  transform: translateY(-5px);
  border-color: var(--violet);
  box-shadow: var(--shadow-md);
}

.field-card:hover::before {
  background: linear-gradient(90deg, var(--violet), var(--yellow));
}

.field-number {
  font-family: var(--font-mono);
  font-size: 0.95rem;
  font-weight: 800;
  color: var(--violet);
  background-color: var(--lavender);
  display: inline-block;
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  margin-bottom: 20px;
  width: fit-content;
}

.field-title {
  font-size: 1.35rem;
  font-weight: 700;
  line-height: 1.25;
  color: var(--charcoal);
  margin-bottom: 14px;
}

.field-desc {
  font-size: 0.96rem;
  line-height: 1.6;
  color: var(--text-light);
  margin-bottom: 24px;
  flex-grow: 1;
}

.field-concepts {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: auto;
  padding-top: 18px;
  border-top: 1px dashed var(--border-subtle);
}

.concept-pill {
  font-size: 0.78rem;
  font-weight: 600;
  padding: 3px 10px;
  border-radius: var(--radius-full);
  background-color: var(--off-white);
  color: var(--charcoal);
  border: 1px solid var(--border);
}

/* ============================================================
   FRAMEWORK SECTION (#framework)
   ============================================================ */
.framework-section {
  background-color: var(--charcoal);
  color: var(--off-white);
  padding: 104px 0;
  position: relative;
  overflow: hidden;
}

.framework-section::after {
  content: "";
  position: absolute;
  top: -150px;
  right: -100px;
  width: 450px;
  height: 450px;
  background: radial-gradient(circle, rgba(118, 103, 245, 0.15) 0%, transparent 70%);
  pointer-events: none;
}

.framework-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;
}

.framework-card {
  background-color: var(--charcoal-card);
  border: 1.5px solid var(--border-dark);
  border-radius: var(--radius-lg);
  padding: 32px 26px;
  display: flex;
  flex-direction: column;
  transition: transform var(--transition), border-color var(--transition), background-color var(--transition);
  position: relative;
}

.framework-card:hover {
  transform: translateY(-4px);
  border-color: var(--violet);
  background-color: #262B38;
}

.framework-num {
  font-family: var(--font-mono);
  font-size: 1.5rem;
  font-weight: 800;
  color: var(--yellow);
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.framework-step-title {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--off-white);
  margin-bottom: 14px;
}

.framework-step-text {
  font-size: 0.96rem;
  line-height: 1.65;
  color: #B2B6C4;
}

/* ============================================================
   CONTRIBUTORS SECTION (#contributors)
   ============================================================ */
.contributors-section {
  padding: 96px 0;
  background-color: var(--off-white);
}

.contributors-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  margin-bottom: 40px;
}

.contributor-card {
  background-color: var(--white);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 30px;
  display: flex;
  flex-direction: column;
  transition: transform var(--transition), border-color var(--transition), box-shadow var(--transition);
}

.contributor-card:hover {
  transform: translateY(-4px);
  border-color: var(--violet);
  box-shadow: var(--shadow-md);
}

.contributor-top {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 18px;
}

/* Typographic Avatar with Initials */
.avatar-initials {
  width: 52px;
  height: 52px;
  border-radius: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: 1.15rem;
  font-weight: 800;
  letter-spacing: 0.04em;
  color: var(--white);
  flex-shrink: 0;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
}

.avatar-cf { background: linear-gradient(135deg, #7667F5, #4D3DCB); }
.avatar-ak { background: linear-gradient(135deg, #38A3C4, #1B7A99); }
.avatar-ki { background: linear-gradient(135deg, #E69D1E, #B8760A); }
.avatar-tc { background: linear-gradient(135deg, #4A5568, #2D3748); }
.avatar-df { background: linear-gradient(135deg, #6C5CE7, #4834D4); }
.avatar-jp { background: linear-gradient(135deg, #2D98DA, #1B6594); }

.contributor-meta {
  flex-grow: 1;
}

.contributor-name {
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--charcoal);
  line-height: 1.2;
}

.contributor-institution {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--muted);
  margin-top: 4px;
}

.contributor-area {
  font-size: 0.86rem;
  font-weight: 700;
  color: var(--violet);
  margin-bottom: 12px;
}

.contributor-bio {
  font-size: 0.94rem;
  line-height: 1.6;
  color: var(--text-light);
  margin-bottom: 20px;
  flex-grow: 1;
}

.contributor-contact-box {
  margin-top: auto;
  padding-top: 14px;
  border-top: 1px solid var(--border-subtle);
}

.platform-badge {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--charcoal);
  background-color: var(--ice-subtle);
  border: 1px solid var(--ice);
  padding: 2px 8px;
  border-radius: var(--radius-xs);
  margin-bottom: 6px;
}

.contact-email-link {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--charcoal);
  text-decoration: none;
  word-break: break-all;
  transition: color var(--transition-fast);
}

.contact-email-link:hover {
  color: var(--violet);
  text-decoration: underline;
}

/* Independence Note Box */
.independence-box {
  background-color: var(--white);
  border: 1.5px solid var(--border);
  border-left: 5px solid var(--yellow);
  border-radius: var(--radius-md);
  padding: 24px 28px;
  box-shadow: var(--shadow-sm);
}

.independence-title {
  font-size: 1.05rem;
  font-weight: 800;
  color: var(--charcoal);
  margin-bottom: 10px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.independence-text {
  font-size: 0.95rem;
  line-height: 1.65;
  color: var(--text-light);
  margin-bottom: 10px;
}

.independence-text:last-child {
  margin-bottom: 0;
}

/* ============================================================
   LEARNING LIBRARY SECTION (#library)
   ============================================================ */
.library-section {
  padding: 96px 0;
  background-color: #F1F1EB;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.library-search-wrapper {
  margin-bottom: 36px;
  max-width: 640px;
}

.search-input-container {
  position: relative;
  display: flex;
  align-items: center;
}

.search-icon {
  position: absolute;
  left: 18px;
  width: 20px;
  height: 20px;
  stroke: var(--muted);
  pointer-events: none;
}

.search-input {
  width: 100%;
  padding: 16px 20px 16px 50px;
  font-family: var(--font-sans);
  font-size: 1rem;
  color: var(--charcoal);
  background-color: var(--white);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-full);
  outline: none;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
  box-shadow: var(--shadow-sm);
}

.search-input:focus {
  border-color: var(--violet);
  box-shadow: 0 0 0 4px var(--violet-glow);
}

.search-input::placeholder {
  color: var(--muted);
}

.clear-search-btn {
  position: absolute;
  right: 16px;
  background: none;
  border: none;
  cursor: pointer;
  color: var(--muted);
  padding: 4px;
  border-radius: 50%;
  display: none;
  align-items: center;
  justify-content: center;
}

.clear-search-btn:hover {
  color: var(--charcoal);
  background-color: var(--border-subtle);
}

/* Library Accordion List */
.library-accordion-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.library-item {
  background-color: var(--white);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.library-item:hover {
  border-color: #B7B4EB;
}

.library-item[open] {
  border-color: var(--violet);
  box-shadow: var(--shadow-sm);
}

.library-summary {
  padding: 20px 24px;
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--charcoal);
  cursor: pointer;
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  user-select: none;
}

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

.summary-title {
  display: flex;
  align-items: center;
  gap: 12px;
}

.summary-index {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--violet);
  background-color: var(--lavender);
  padding: 3px 8px;
  border-radius: var(--radius-xs);
}

.summary-icon {
  width: 22px;
  height: 22px;
  stroke: var(--violet);
  transition: transform var(--transition);
  flex-shrink: 0;
}

.library-item[open] .summary-icon {
  transform: rotate(180deg);
}

.library-content {
  padding: 0 24px 24px;
  color: var(--text-light);
  font-size: 1rem;
  line-height: 1.7;
  border-top: 1px solid var(--border-subtle);
  margin-top: 8px;
  padding-top: 16px;
}

.library-content p {
  margin-bottom: 12px;
}

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

.library-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 14px;
}

.library-tag {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  background-color: var(--off-white);
  color: var(--charcoal);
  border: 1px solid var(--border);
  padding: 2px 8px;
  border-radius: var(--radius-xs);
}

/* No Results Message */
.no-results-box {
  display: none;
  padding: 36px 24px;
  background-color: var(--white);
  border: 1.5px dashed var(--border);
  border-radius: var(--radius-md);
  text-align: center;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--muted);
}

/* ============================================================
   ABOUT SECTION (#about)
   ============================================================ */
.about-section {
  padding: 104px 0;
  background-color: var(--white);
}

.about-grid {
  display: grid;
  grid-template-columns: 0.8fr 1.2fr;
  align-items: center;
  gap: 64px;
}

.about-visual-col {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.about-mark-img {
  width: 200px;
  height: 200px;
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg);
  border: 2px solid var(--charcoal);
}

.about-content-col {
  display: flex;
  flex-direction: column;
}

.about-lead-text {
  font-size: 1.12rem;
  line-height: 1.7;
  color: var(--text);
  margin-bottom: 24px;
}

.about-not-box {
  background-color: var(--off-white);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-md);
  padding: 24px 28px;
  margin-top: 10px;
}

.not-title {
  font-size: 0.98rem;
  font-weight: 700;
  color: var(--charcoal);
  margin-bottom: 12px;
}

.not-list {
  list-style: none;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 8px 20px;
}

.not-list li {
  position: relative;
  padding-left: 20px;
  font-size: 0.92rem;
  color: var(--muted);
}

.not-list li::before {
  content: "×";
  position: absolute;
  left: 0;
  top: -1px;
  color: #D9534F;
  font-weight: 800;
  font-size: 1.1rem;
}

/* ============================================================
   FOOTER
   ============================================================ */
.site-footer {
  background-color: var(--charcoal);
  color: #A0A5B5;
  padding: 64px 0 32px;
  border-top: 1px solid var(--border-dark);
}

.footer-top-grid {
  display: grid;
  grid-template-columns: 1.5fr 1fr;
  gap: 48px;
  margin-bottom: 48px;
  align-items: start;
}

.footer-brand-title {
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--off-white);
  letter-spacing: -0.01em;
  margin-bottom: 12px;
}

.footer-desc {
  font-size: 0.95rem;
  line-height: 1.6;
  max-width: 480px;
  color: #A0A5B5;
}

.footer-nav-col {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.footer-nav-title {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--ice);
  margin-bottom: 4px;
}

.footer-links-list {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 12px 20px;
}

.footer-link {
  color: #C2C6D4;
  text-decoration: none;
  font-size: 0.92rem;
  transition: color var(--transition-fast);
}

.footer-link:hover {
  color: var(--yellow);
}

.footer-bottom {
  padding-top: 24px;
  border-top: 1px solid var(--border-dark);
  text-align: center;
}

.footer-copyright {
  font-size: 0.88rem;
  color: #7E8496;
}

/* ============================================================
   BACK TO TOP BUTTON
   ============================================================ */
.back-to-top-btn {
  position: fixed;
  bottom: 28px;
  right: 28px;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background-color: var(--charcoal);
  color: var(--yellow);
  border: 1.5px solid var(--border-dark);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  box-shadow: var(--shadow-md);
  opacity: 0;
  visibility: hidden;
  transform: translateY(16px);
  transition: opacity var(--transition), visibility var(--transition), transform var(--transition), background-color var(--transition-fast);
  z-index: 900;
}

.back-to-top-btn.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top-btn:hover {
  background-color: var(--violet);
  color: var(--white);
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
}

.back-to-top-btn svg {
  width: 20px;
  height: 20px;
  stroke: currentColor;
  stroke-width: 2.5;
}

/* ============================================================
   REVEAL ANIMATIONS (IntersectionObserver)
   ============================================================ */
.reveal {
  opacity: 0;
  transform: translateY(22px);
  transition: opacity 0.6s cubic-bezier(0.16, 1, 0.3, 1), transform 0.6s cubic-bezier(0.16, 1, 0.3, 1);
}

.reveal.is-revealed {
  opacity: 1;
  transform: translateY(0);
}

@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;
  }
  .reveal {
    opacity: 1 !important;
    transform: none !important;
  }
  .floating-badge {
    animation: none !important;
  }
}

/* ============================================================
   RESPONSIVE DESIGN BREAKPOINTS
   ============================================================ */

/* Tablet Breakpoint (max-width: 950px) */
@media (max-width: 950px) {
  .hero-grid {
    grid-template-columns: 1fr;
    gap: 40px;
  }

  .hero-visual-stage {
    order: -1;
    padding: 16px 0;
  }

  .hero-circuit-card {
    max-width: 340px;
  }

  .fields-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
  }

  .framework-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
  }

  .contributors-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
  }

  .about-grid {
    grid-template-columns: 1fr;
    gap: 40px;
    text-align: left;
  }

  .about-visual-col {
    order: -1;
  }

  .footer-top-grid {
    grid-template-columns: 1fr;
    gap: 32px;
  }
}

/* Mobile Breakpoint (max-width: 650px) */
@media (max-width: 650px) {
  .nav-desktop {
    display: none;
  }

  .mobile-toggle {
    display: flex;
  }

  .nav-mobile {
    display: block;
  }

  .hero-section {
    padding-top: 36px;
    padding-bottom: 50px;
  }

  .hero-title {
    font-size: 2.1rem;
  }

  .hero-desc {
    font-size: 1.05rem;
  }

  .btn-group {
    flex-direction: column;
    align-items: stretch;
  }

  .btn {
    width: 100%;
  }

  .floating-badge {
    font-size: 0.75rem;
    padding: 6px 12px;
  }

  .badge-structure { top: -6px; left: -4px; }
  .badge-signal { top: 8px; right: -8px; }
  .badge-interaction { bottom: 12px; left: -10px; }
  .badge-practice { bottom: -6px; right: 4px; }

  .principles-flow {
    flex-direction: column;
    gap: 10px;
  }

  .principles-strip .principle-separator {
    transform: rotate(90deg);
  }

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

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

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

  .not-list {
    grid-template-columns: 1fr;
  }

  .back-to-top-btn {
    bottom: 20px;
    right: 20px;
    width: 44px;
    height: 44px;
  }
}