/* ============================================================
   Lumen Edge — AI-Native Learning Platform Design System
   "Serious learning, deep thinking, engineering excellence."
   ============================================================ */

/* --- Google Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Space+Grotesk:wght@400;500;600;700&family=Inter:wght@300;400;500;600&family=JetBrains+Mono:wght@400;500&display=swap');

/* --- Design Tokens --- */
:root {
  /* Surfaces */
  --surface-000: #0A0A0C;
  --surface-100: #111114;
  --surface-200: #18181C;
  --surface-300: #1F1F24;
  --surface-400: #28282E;

  /* Text */
  --text-primary: #F0F0F2;
  --text-secondary: #A0A0A8;
  --text-tertiary: #6B6B74;
  --text-disabled: #45454D;

  /* Accent */
  --accent-primary: #E8E8EC;
  --accent-hover: #FFFFFF;
  --accent-muted: #3A3A42;
  --accent-ice: #B8C4D0;
  --accent-ice-dim: #8A9AAD;

  /* Semantic */
  --color-success: #4ADE80;
  --color-success-dim: #22543D;
  --color-warning: #FBBF24;
  --color-warning-dim: #422006;
  --color-error: #F87171;
  --color-error-dim: #450A0A;
  --color-info: #60A5FA;
  --color-info-dim: #1E3A5F;

  /* Glow & Illumination */
  --glow-subtle: rgba(255, 255, 255, 0.03);
  --glow-medium: rgba(255, 255, 255, 0.06);
  --glow-accent: rgba(184, 196, 208, 0.08);
  --illumination-card: radial-gradient(ellipse 80% 50% at 50% 120%, rgba(255, 255, 255, 0.05) 0%, transparent 60%);

  /* Borders */
  --border-hairline: 1px solid rgba(255, 255, 255, 0.06);
  --border-subtle: 1px solid rgba(255, 255, 255, 0.08);
  --border-medium: 1px solid rgba(255, 255, 255, 0.12);
  --border-glow: 1px solid rgba(184, 196, 208, 0.15);

  /* Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.5);
  --shadow-xl: 0 16px 48px rgba(0, 0, 0, 0.6);

  /* Layout */
  --max-width: 1200px;

  /* Motion */
  --duration-fast: 100ms;
  --duration-normal: 200ms;
  --duration-slow: 300ms;
  --ease-default: cubic-bezier(0.25, 0.1, 0.25, 1);
  --ease-out: cubic-bezier(0, 0, 0.2, 1);

  /* Fonts */
  --font-display: 'Space Grotesk', 'Inter', system-ui, sans-serif;
  --font-body: 'Inter', 'Space Grotesk', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'SF Mono', monospace;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  background: var(--surface-000);
  color: var(--text-primary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-size: 14px;
}

/* --- Base Elements --- */
a {
  color: var(--accent-ice);
  text-decoration: none;
  transition: color var(--duration-normal) var(--ease-default);
}

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

code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: var(--surface-200);
  padding: 2px 7px;
  border-radius: var(--radius-sm);
  border: var(--border-hairline);
}

pre {
  font-family: 'SF Mono', 'Menlo', 'Consolas', 'Liberation Mono', monospace;
  font-size: 0.82em;
  background: var(--surface-000);
  border: var(--border-hairline);
  border-radius: var(--radius-md);
  padding: 1.2em 1.4em;
  overflow-x: auto;
  line-height: 1.6;
  position: relative;
  tab-size: 4;
}

pre code {
  background: none;
  padding: 0;
  border: none;
  font-size: inherit;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.2rem 0;
}

th,
td {
  border: var(--border-hairline);
  padding: 0.65rem 1rem;
  text-align: left;
}

th {
  background: var(--surface-100);
  font-weight: 600;
  font-size: 0.85rem;
  font-family: var(--font-display);
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

td {
  color: var(--text-secondary);
  font-size: 0.88rem;
}

/* === Layout === */

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 2rem;
}

/* === Navigation === */

.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background: rgba(10, 10, 12, 0.92);
  backdrop-filter: blur(16px) saturate(1.5);
  -webkit-backdrop-filter: blur(16px) saturate(1.5);
  border-bottom: var(--border-hairline);
  height: 64px;
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.nav-logo {
  font-family: var(--font-display);
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  letter-spacing: -0.01em;
}

.nav-logo span {
  color: var(--accent-ice);
  font-family: var(--font-mono);
  font-size: 0.9rem;
  opacity: 0.7;
}

.nav-links {
  display: flex;
  gap: 2rem;
  list-style: none;
}

.nav-links a {
  color: var(--text-tertiary);
  font-size: 0.85rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  transition: color var(--duration-normal) var(--ease-default);
}

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

/* === Hero === */

.hero {
  padding: 8rem 0 5rem;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: "";
  position: absolute;
  bottom: -40%;
  left: 50%;
  transform: translateX(-50%);
  width: 900px;
  height: 500px;
  background: radial-gradient(ellipse, rgba(184, 196, 208, 0.06) 0%, transparent 70%);
  pointer-events: none;
}

.hero h1 {
  font-family: var(--font-display);
  font-size: 3.2rem;
  font-weight: 700;
  line-height: 1.1;
  margin-bottom: 1.2rem;
  letter-spacing: -0.025em;
  color: var(--text-primary);
}

.hero .subtitle {
  font-size: 1.05rem;
  color: var(--text-secondary);
  max-width: 580px;
  margin: 0 auto 2.5rem;
  line-height: 1.65;
}

.hero-badges {
  display: flex;
  gap: 0.6rem;
  justify-content: center;
  flex-wrap: wrap;
  margin-bottom: 2.5rem;
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.3rem 0.85rem;
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 500;
  letter-spacing: 0.03em;
  border: var(--border-hairline);
  background: var(--surface-100);
  color: var(--text-secondary);
  font-family: var(--font-body);
}

.badge .dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
}

.badge .dot.green { background: var(--color-success); }
.badge .dot.yellow { background: var(--color-warning); }
.badge .dot.cyan { background: var(--accent-ice); }

.hero-actions {
  display: flex;
  gap: 0.75rem;
  justify-content: center;
}

/* === Buttons === */

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0 20px;
  height: 40px;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-weight: 500;
  font-family: var(--font-body);
  transition: all var(--duration-normal) var(--ease-out);
  border: none;
  cursor: pointer;
  letter-spacing: 0.01em;
}

.btn-primary {
  background: var(--accent-primary);
  color: var(--surface-000);
}

.btn-primary:hover {
  background: var(--accent-hover);
  color: var(--surface-000);
  box-shadow: var(--shadow-md), 0 0 20px rgba(232, 232, 236, 0.08);
}

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

.btn-secondary {
  background: transparent;
  color: var(--text-primary);
  border: var(--border-subtle);
}

.btn-secondary:hover {
  background: var(--surface-200);
  border-color: rgba(255, 255, 255, 0.12);
  color: var(--text-primary);
}

/* === Sections === */

section {
  padding: 5rem 0;
}

.section-title {
  font-family: var(--font-display);
  font-size: 1.85rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
  letter-spacing: -0.015em;
}

.section-desc {
  color: var(--text-secondary);
  margin-bottom: 2.5rem;
  max-width: 560px;
  font-size: 0.92rem;
  line-height: 1.6;
}

/* === Formula Box === */

.formula-box {
  background: var(--surface-100);
  border: var(--border-hairline);
  border-radius: var(--radius-md);
  padding: 2rem 2.5rem;
  text-align: center;
  margin: 2rem 0;
  font-family: var(--font-mono);
  font-size: 1rem;
  position: relative;
  overflow: hidden;
}

.formula-box::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: var(--illumination-card);
  pointer-events: none;
}

.formula-box .label {
  display: block;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-tertiary);
  margin-bottom: 0.6rem;
  font-family: var(--font-body);
  font-weight: 500;
}

.formula-box .eq {
  font-size: 1.15rem;
  color: var(--accent-ice);
  font-weight: 500;
  position: relative;
  z-index: 1;
}

/* === Architecture Grid === */

.arch-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 1rem;
  margin: 2rem 0;
}

.arch-card {
  background: var(--surface-100);
  border: var(--border-hairline);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  transition: all var(--duration-normal) var(--ease-out);
  position: relative;
  overflow: hidden;
}

.arch-card::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: var(--illumination-card);
  pointer-events: none;
  opacity: 0;
  transition: opacity var(--duration-normal) var(--ease-out);
}

.arch-card:hover {
  border-color: rgba(255, 255, 255, 0.1);
  background: var(--surface-200);
  box-shadow: var(--shadow-md);
}

.arch-card:hover::after {
  opacity: 1;
}

.arch-card .icon {
  font-size: 1.6rem;
  margin-bottom: 0.8rem;
}

.arch-card h3 {
  font-family: var(--font-display);
  font-size: 0.95rem;
  font-weight: 600;
  margin-bottom: 0.4rem;
  letter-spacing: -0.005em;
}

.arch-card p {
  font-size: 0.82rem;
  color: var(--text-secondary);
  line-height: 1.55;
}

.arch-card pre {
  margin: 0.6rem 0;
  font-size: 0.78em;
  background: var(--surface-000);
  padding: 0.8em 1em;
}

/* === Learning Path === */

.path {
  display: flex;
  flex-direction: column;
  gap: 0;
  position: relative;
}

.path::before {
  content: "";
  position: absolute;
  left: 24px;
  top: 40px;
  bottom: 40px;
  width: 1px;
  background: linear-gradient(to bottom, var(--accent-ice), transparent);
  opacity: 0.15;
}

.path-item {
  display: grid;
  grid-template-columns: 50px 1fr;
  gap: 1.2rem;
  padding: 0.6rem 0;
  position: relative;
}

.path-dot {
  width: 50px;
  display: flex;
  justify-content: center;
  padding-top: 1.3rem;
}

.path-dot span {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--surface-100);
  border: 2px solid var(--surface-400);
  display: block;
  z-index: 1;
  transition: all var(--duration-normal) var(--ease-out);
}

.path-item:hover .path-dot span {
  border-color: var(--accent-ice);
  background: var(--accent-ice);
  box-shadow: 0 0 10px rgba(184, 196, 208, 0.2);
}

.path-content {
  background: var(--surface-100);
  border: var(--border-hairline);
  border-radius: var(--radius-md);
  padding: 1.2rem 1.5rem;
  transition: all var(--duration-normal) var(--ease-out);
  cursor: default;
  position: relative;
  overflow: hidden;
  text-decoration: none;
  color: inherit;
  display: block;
}

.path-content::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: var(--illumination-card);
  pointer-events: none;
  opacity: 0;
  transition: opacity var(--duration-normal) var(--ease-out);
}

.path-item:hover .path-content {
  border-color: rgba(255, 255, 255, 0.1);
  background: var(--surface-200);
}

.path-item:hover .path-content::after {
  opacity: 1;
}

.path-header {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  margin-bottom: 0.4rem;
}

.path-num {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 500;
  color: var(--accent-ice);
  background: rgba(184, 196, 208, 0.08);
  padding: 0.15rem 0.5rem;
  border-radius: var(--radius-sm);
  letter-spacing: 0.04em;
}

.path-title {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 0.95rem;
  letter-spacing: -0.005em;
}

.path-desc {
  font-size: 0.82rem;
  color: var(--text-secondary);
  margin-bottom: 0.6rem;
  line-height: 1.55;
}

.path-tags {
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
}

.tag {
  font-size: 0.68rem;
  font-weight: 500;
  padding: 0.15rem 0.55rem;
  border-radius: var(--radius-sm);
  background: var(--surface-200);
  color: var(--text-tertiary);
  border: var(--border-hairline);
  letter-spacing: 0.02em;
}

.tag.highlight {
  color: var(--color-warning);
  border-color: rgba(251, 191, 36, 0.15);
  background: rgba(251, 191, 36, 0.06);
}

/* === Detail Page === */

.detail-hero {
  padding: 6.5rem 0 2rem;
  border-bottom: var(--border-hairline);
}

.breadcrumb {
  font-size: 0.8rem;
  color: var(--text-tertiary);
  margin-bottom: 1rem;
  font-weight: 400;
}

.breadcrumb a {
  color: var(--text-tertiary);
  transition: color var(--duration-normal) var(--ease-default);
}

.breadcrumb a:hover {
  color: var(--text-secondary);
}

.detail-hero h1 {
  font-family: var(--font-display);
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 0.8rem;
  letter-spacing: -0.02em;
}

.detail-hero .meta {
  display: flex;
  gap: 1.5rem;
  color: var(--text-tertiary);
  font-size: 0.82rem;
  font-weight: 400;
}

.detail-hero .meta span {
  display: flex;
  align-items: center;
  gap: 0.3rem;
}

.detail-layout {
  display: grid;
  grid-template-columns: 1fr 260px;
  gap: 3rem;
  padding: 3rem 0;
}

.detail-main {
  min-width: 0;
}

.detail-sidebar {
  position: sticky;
  top: 88px;
  align-self: start;
}

/* === Table of Contents === */

.toc {
  background: var(--surface-100);
  border: var(--border-hairline);
  border-radius: var(--radius-md);
  padding: 1.2rem;
}

.toc h4 {
  font-family: var(--font-display);
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-tertiary);
  margin-bottom: 0.8rem;
  font-weight: 500;
}

.toc ul {
  list-style: none;
}

.toc li {
  padding: 0.25rem 0;
}

.toc a {
  font-size: 0.82rem;
  color: var(--text-tertiary);
  transition: color var(--duration-normal) var(--ease-default);
  display: block;
  padding: 0.15rem 0.6rem;
  border-left: 2px solid transparent;
  margin-left: -1px;
}

.toc a:hover {
  color: var(--text-primary);
  border-left-color: var(--surface-400);
}

/* === Content Sections === */

.content-section {
  margin-bottom: 3rem;
}

.content-section h2 {
  font-family: var(--font-display);
  font-size: 1.35rem;
  font-weight: 700;
  margin-bottom: 1rem;
  padding-bottom: 0.6rem;
  border-bottom: var(--border-hairline);
  letter-spacing: -0.01em;
}

.content-section h3 {
  font-family: var(--font-display);
  font-size: 1.05rem;
  font-weight: 600;
  margin: 1.5rem 0 0.8rem;
  letter-spacing: -0.005em;
}

.content-section p {
  margin-bottom: 1rem;
  color: var(--text-secondary);
  line-height: 1.7;
  font-size: 0.9rem;
}

.content-section ul,
.content-section ol {
  margin-bottom: 1rem;
  padding-left: 1.5rem;
  color: var(--text-secondary);
  font-size: 0.9rem;
}

.content-section li {
  margin-bottom: 0.35rem;
  line-height: 1.65;
}

.content-section pre {
  margin-bottom: 1.5rem;
}

/* === Diagram === */

.diagram {
  background: var(--surface-000);
  border: var(--border-hairline);
  border-radius: var(--radius-md);
  padding: 1.2rem 1.4rem;
  margin: 1.2rem 0;
  font-family: 'SF Mono', 'Menlo', 'Consolas', 'Liberation Mono', monospace;
  font-size: 0.82em;
  line-height: 1.2;
  white-space: pre;
  overflow-x: auto;
  color: var(--text-tertiary);
  letter-spacing: 0;
  word-spacing: 0;
  tab-size: 4;
}

.diagram-rendered {
  background: none;
  border: none;
  padding: 0;
  margin: 1.5rem 0;
  white-space: normal;
}

.diagram-rendered svg {
  display: block;
  max-width: 100%;
  height: auto;
  border-radius: var(--radius-md);
  overflow: visible;
}

/* === Page Navigation === */

.page-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: var(--border-hairline);
}

.page-nav a {
  display: block;
  padding: 1rem 1.2rem;
  background: var(--surface-100);
  border: var(--border-hairline);
  border-radius: var(--radius-md);
  transition: all var(--duration-normal) var(--ease-out);
  position: relative;
  overflow: hidden;
}

.page-nav a::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: var(--illumination-card);
  pointer-events: none;
  opacity: 0;
  transition: opacity var(--duration-normal) var(--ease-out);
}

.page-nav a:hover {
  border-color: rgba(255, 255, 255, 0.1);
  background: var(--surface-200);
}

.page-nav a:hover::after {
  opacity: 1;
}

.page-nav .label {
  font-size: 0.7rem;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-weight: 500;
}

.page-nav .name {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 0.92rem;
  margin-top: 0.2rem;
  letter-spacing: -0.005em;
}

.page-nav .next {
  text-align: right;
}

/* === Footer === */

.footer {
  padding: 3rem 0;
  border-top: var(--border-hairline);
  text-align: center;
  color: var(--text-tertiary);
  font-size: 0.8rem;
}

/* === Responsive === */

@media (max-width: 900px) {
  .hero h1 { font-size: 2.4rem; }
  .detail-layout { grid-template-columns: 1fr; }
  .detail-sidebar { display: none; }
  .path::before { left: 18px; }
  .path-dot { width: 38px; }
  .diagram-rendered { overflow-x: auto; }
  .diagram-rendered svg { min-width: 480px; }
}

@media (max-width: 600px) {
  .nav-links { display: none; }
  .hero { padding: 5.5rem 0 2.5rem; }
  .hero h1 { font-size: 1.85rem; }
  .container { padding: 0 1rem; }
  .hero-actions { flex-direction: column; align-items: center; }
  .page-nav { grid-template-columns: 1fr; }
  .hero-badges { gap: 0.4rem; }
  .detail-hero .meta { flex-wrap: wrap; gap: 0.8rem; }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}