/* ==========================================================================
   赔钱机场 (PEIQIAN / NETWORK) - SET 3: STACKED SHEET INTERFACE
   A technical paper, layered document & specification sheet design system.
   Strictly HTML5, Vanilla CSS, Clean Typography, Zero UI Bloat.
   ========================================================================== */

:root {
  /* Core Paper & Document Palette (75% Paper/Warm White, 20% Text/Border, 5% Accents) */
  --bg-page: #F3EFE6;
  --bg-sheet: #FFFDFC;
  --bg-paper: #FAF8F3;
  --bg-paper-gray: #ECE8DF;
  --bg-paper-subtle: #F6F2EA;
  --bg-footer: #E9E4DA;

  /* Typography Colors */
  --text-main: #171717;
  --text-body: #4A4C49;
  --text-secondary: #777972;
  --text-muted: #8E9189;

  /* Precision Document Accents (5%) */
  --doc-red: #C74732;
  --doc-red-bg: #FDF2F0;
  --steel-blue: #4B6573;
  --steel-blue-bg: #EDF3F7;
  --muted-olive: #6E7862;
  --muted-olive-bg: #F0F3ED;

  /* Lines & Paper Geometry */
  --border-sheet: #D8D3C8;
  --border-light: #E6E2D8;
  --border-dark: #AFA99E;
  --radius-sheet: 4px;
  --radius-sm: 2px;
  --shadow-sheet: 0 10px 30px rgba(20, 20, 20, 0.05);
  --shadow-tab: 0 -3px 8px rgba(20, 20, 20, 0.03);

  /* Fonts */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;

  /* Layout Max Width */
  --site-max-width: 1160px;
}

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

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

body {
  font-family: var(--font-sans);
  background-color: var(--bg-page);
  color: var(--text-body);
  line-height: 1.65;
  font-weight: 400;
  overflow-x: hidden;
}

/* Accessibility & Focus */
a {
  color: inherit;
  text-decoration: none;
  transition: color 0.15s ease, border-color 0.15s ease;
}

a:focus-visible, button:focus-visible, summary:focus-visible {
  outline: 2px solid var(--doc-red);
  outline-offset: 2px;
}

img, picture, svg {
  display: block;
  max-width: 100%;
}

/* Monospace & Document Codes */
.mono-tag {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-secondary);
}

.mono-red {
  color: var(--doc-red);
}

.mono-blue {
  color: var(--steel-blue);
}

.mono-olive {
  color: var(--muted-olive);
}

/* Main Container */
.container {
  width: 100%;
  max-width: var(--site-max-width);
  margin-left: auto;
  margin-right: auto;
  padding-left: 20px;
  padding-right: 20px;
}

/* ==========================================================================
   HEADER: DOCUMENT BAR
   ========================================================================== */
.document-bar {
  position: sticky;
  top: 0;
  z-index: 1000;
  height: 64px;
  background-color: var(--bg-paper);
  border-bottom: 1px solid var(--border-sheet);
  display: flex;
  align-items: center;
}

.bar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  height: 100%;
}

.bar-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--text-main);
  letter-spacing: -0.01em;
}

.bar-brand .brand-badge {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  font-weight: 500;
  color: var(--doc-red);
  border: 1px solid var(--border-sheet);
  padding: 2px 6px;
  border-radius: var(--radius-sm);
  background: var(--bg-sheet);
}

.bar-center {
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.1em;
  color: var(--text-secondary);
}

.bar-actions {
  display: flex;
  align-items: center;
  gap: 14px;
}

.btn-index {
  background: transparent;
  border: 1px solid var(--border-sheet);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 600;
  padding: 6px 14px;
  color: var(--text-main);
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  border-radius: var(--radius-sm);
  transition: all 0.15s ease;
}

.btn-index:hover {
  background: var(--bg-paper-gray);
  border-color: var(--border-dark);
}

.btn-cta {
  background: var(--text-main);
  color: #FFFDFC;
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 600;
  padding: 7px 16px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--text-main);
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: all 0.15s ease;
}

.btn-cta:hover {
  background: #333;
  color: #FFFDFC;
}

.btn-cta-red {
  background: var(--doc-red);
  border-color: var(--doc-red);
  color: #FFFDFC;
}

.btn-cta-red:hover {
  background: #ad3b28;
  color: #FFFDFC;
}

/* Document Index Drawer / Modal */
.index-drawer {
  position: fixed;
  top: 64px;
  left: 0;
  width: 100%;
  background: var(--bg-paper);
  border-bottom: 2px solid var(--border-sheet);
  box-shadow: 0 16px 36px rgba(0, 0, 0, 0.08);
  padding: 30px 20px;
  z-index: 999;
  display: none;
}

.index-drawer.is-active {
  display: block;
}

.index-drawer-inner {
  max-width: var(--site-max-width);
  margin: 0 auto;
}

.index-drawer-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-bottom: 16px;
  margin-bottom: 20px;
  border-bottom: 1px solid var(--border-light);
}

.index-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 16px;
}

.index-item {
  display: block;
  background: var(--bg-sheet);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  padding: 14px 16px;
  transition: all 0.15s ease;
}

.index-item:hover {
  border-color: var(--text-main);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0,0,0,0.04);
}

.index-item-code {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--doc-red);
  margin-bottom: 4px;
}

.index-item-title {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-main);
}

.index-item-desc {
  font-size: 0.78rem;
  color: var(--text-secondary);
  margin-top: 4px;
}

/* ==========================================================================
   STACKED SHEETS ARCHITECTURE & CORE GEOMETRY
   ========================================================================== */
.sheet-stack-wrapper {
  padding-top: 40px;
  padding-bottom: 60px;
}

/* Base Sheet Styling */
.sheet {
  background: var(--bg-sheet);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  box-shadow: var(--shadow-sheet);
  position: relative;
  margin-bottom: 50px;
}

/* Sheet Tab on Top */
.sheet-tab-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 24px;
  background: var(--bg-paper);
  border-bottom: 1px solid var(--border-sheet);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.06em;
}

.sheet-tab-title {
  font-weight: 600;
  color: var(--text-main);
  text-transform: uppercase;
}

.sheet-tab-right {
  display: flex;
  align-items: center;
  gap: 12px;
  color: var(--text-secondary);
}

.sheet-content {
  padding: 36px 40px;
}

/* Layer Offset Rules for Desktop (Section 15 & 16) */
.sheet-offset-0 {
  margin-left: 0;
}

.sheet-offset-1 {
  margin-left: 32px;
  max-width: calc(100% - 32px);
}

.sheet-offset-2 {
  margin-left: 12px;
  max-width: calc(100% - 12px);
}

.sheet-offset-3 {
  margin-left: 44px;
  max-width: calc(100% - 44px);
}

.sheet-offset-4 {
  margin-left: 16px;
  max-width: calc(100% - 16px);
}

.sheet-offset-5 {
  margin-left: 28px;
  max-width: calc(100% - 28px);
}

/* ==========================================================================
   HERO SECTION: STACKED COVER SHEET (Sections 21-32)
   ========================================================================== */
.hero-stack-container {
  position: relative;
  padding-top: 56px; /* Room for underlay tabs */
  margin-bottom: 50px;
}

/* Underlay Tabs peeking behind main cover */
.hero-underlay-tab {
  position: absolute;
  left: 0;
  right: 0;
  height: 44px;
  border: 1px solid var(--border-sheet);
  border-bottom: none;
  border-radius: var(--radius-sheet) var(--radius-sheet) 0 0;
  display: flex;
  align-items: flex-start;
  padding: 8px 24px;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  color: var(--text-secondary);
}

.tab-level-3 {
  top: 0;
  left: 28px;
  right: 28px;
  background-color: var(--bg-paper-gray);
  z-index: 1;
}

.tab-level-2 {
  top: 24px;
  left: 14px;
  right: 14px;
  background-color: var(--bg-paper-subtle);
  z-index: 2;
}

/* Hero Top Sheet (Cover) */
.hero-cover-sheet {
  position: relative;
  z-index: 3;
  background: var(--bg-sheet);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  box-shadow: var(--shadow-sheet);
}

.hero-content {
  padding: 44px 48px 36px 48px;
}

.hero-main-title {
  font-size: clamp(2rem, 3.8vw, 3.25rem); /* 36px - 52px */
  font-weight: 700;
  color: var(--text-main);
  line-height: 1.18;
  letter-spacing: -0.02em;
  margin-bottom: 12px;
}

.hero-tagline {
  display: block;
  font-size: clamp(1.8rem, 3.4vw, 2.8rem);
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 16px;
  line-height: 1.2;
}

.hero-subtitle {
  font-size: clamp(1.15rem, 1.8vw, 1.45rem);
  font-weight: 500;
  color: var(--steel-blue);
  margin-bottom: 18px;
}

.hero-geo-text {
  font-size: 1.05rem;
  line-height: 1.7;
  color: var(--text-body);
  max-width: 920px;
  margin-bottom: 32px;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--border-light);
}

/* Hero Specification Layout (Section 29) */
.hero-specs-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
  margin-bottom: 32px;
  background: var(--bg-paper);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  padding: 18px 22px;
}

.hero-spec-col {
  border-right: 1px solid var(--border-light);
  padding-right: 14px;
}

.hero-spec-col:last-child {
  border-right: none;
  padding-right: 0;
}

.hero-spec-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--text-secondary);
  letter-spacing: 0.08em;
  margin-bottom: 6px;
  text-transform: uppercase;
}

.hero-spec-val {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-main);
  line-height: 1.45;
}

/* Hero Action Bar */
.hero-actions {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}

.btn-secondary {
  background: var(--bg-paper);
  border: 1px solid var(--border-sheet);
  color: var(--text-main);
  font-size: 0.9rem;
  font-weight: 600;
  padding: 9px 20px;
  border-radius: var(--radius-sm);
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: all 0.15s ease;
}

.btn-secondary:hover {
  background: var(--bg-paper-gray);
  border-color: var(--border-dark);
}

.btn-text-link {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--steel-blue);
  padding: 8px 12px;
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.btn-text-link:hover {
  color: var(--text-main);
  text-decoration: underline;
}

/* ==========================================================================
   SECTION 01: GLOBAL NETWORK SHEET (DOCUMENT / 002)
   ========================================================================== */
.global-sheet-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 40px;
  position: relative;
}

.global-sheet-grid::after {
  content: "";
  position: absolute;
  top: 0;
  bottom: 0;
  left: 50%;
  width: 1px;
  background-color: var(--border-sheet);
  transform: translateX(-50%);
}

.region-block {
  margin-bottom: 32px;
}

.region-block:last-child {
  margin-bottom: 0;
}

.region-header {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  border-bottom: 1px solid var(--border-sheet);
  padding-bottom: 8px;
  margin-bottom: 16px;
}

.region-name {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-main);
  letter-spacing: 0.02em;
}

.region-count {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--steel-blue);
  font-weight: 600;
}

.node-list {
  list-style: none;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px 16px;
}

.node-item {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.92rem;
  color: var(--text-body);
}

.node-bullet {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background-color: var(--muted-olive);
}

/* ==========================================================================
   SECTION 02: DEVICE SYSTEM SHEET (DOCUMENT / 003)
   ========================================================================== */
.device-spec-list {
  border-top: 1px solid var(--border-sheet);
}

.device-spec-row {
  display: grid;
  grid-template-columns: 60px 160px 140px 1fr 180px;
  align-items: center;
  padding: 16px 10px;
  border-bottom: 1px solid var(--border-light);
  font-size: 0.92rem;
}

.device-spec-row:hover {
  background-color: var(--bg-paper-subtle);
}

.device-id {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.device-name {
  font-weight: 700;
  color: var(--text-main);
  font-size: 1rem;
}

.device-type {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--steel-blue);
}

.device-desc {
  color: var(--text-body);
  font-size: 0.88rem;
}

.device-action {
  text-align: right;
}

.device-action a {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--doc-red);
}

.device-action a:hover {
  text-decoration: underline;
}

/* ==========================================================================
   SECTION 03: AI ENVIRONMENT SHEET (DOCUMENT / 004)
   ========================================================================== */
.ai-sheet-grid {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 36px;
  align-items: center;
}

.ai-tools-list {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
}

.ai-tool-item {
  background: var(--bg-paper);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  padding: 16px 14px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.ai-tool-name {
  font-size: 1rem;
  font-weight: 700;
  color: var(--text-main);
}

.ai-tool-role {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--text-secondary);
}

.ai-doc-note {
  background: var(--bg-paper);
  border-left: 3px solid var(--doc-red);
  padding: 24px;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

.ai-doc-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 8px;
}

.ai-doc-desc {
  font-size: 0.88rem;
  color: var(--text-body);
  line-height: 1.6;
  margin-bottom: 14px;
}

/* ==========================================================================
   SECTION 04: MEDIA SERVICES SHEET (DOCUMENT / 005)
   ========================================================================== */
.media-sheet-content {
  display: flex;
  flex-direction: column;
  gap: 28px;
}

.media-services-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 20px;
  padding: 16px 0;
  border-bottom: 1px solid var(--border-sheet);
}

.media-names {
  display: flex;
  gap: 28px;
  flex-wrap: wrap;
}

.media-item {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text-main);
  letter-spacing: -0.01em;
}

.media-count-badge {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--steel-blue);
  background: var(--steel-blue-bg);
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  font-weight: 600;
}

.media-footer-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 16px;
}

.media-statement {
  font-size: 0.95rem;
  color: var(--text-body);
  max-width: 680px;
}

/* ==========================================================================
   SECTION 05: PLAN SPECIFICATIONS (PRICING) (DOCUMENT / 006)
   ========================================================================== */
.pricing-stack {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
  position: relative;
  align-items: start;
}

.price-spec-sheet {
  background: var(--bg-sheet);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  box-shadow: var(--shadow-sheet);
  position: relative;
  transition: transform 0.15s ease, border-color 0.15s ease;
  overflow: hidden;
}

.price-spec-sheet:hover {
  border-color: var(--border-dark);
}

/* Focus recommended card highlighted */
.price-sheet-focus {
  border: 2px solid var(--doc-red);
  transform: translateY(-8px);
  z-index: 10;
  background: #FFFDFD;
}

.price-sheet-tab {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 14px;
  background: var(--bg-paper);
  border-bottom: 1px solid var(--border-light);
  font-family: var(--font-mono);
  font-size: 0.72rem;
}

.price-sheet-focus .price-sheet-tab {
  background: var(--doc-red-bg);
}

.rec-pill {
  background: var(--doc-red);
  color: #FFFDFC;
  font-size: 0.65rem;
  font-weight: 700;
  padding: 2px 6px;
  border-radius: var(--radius-sm);
  letter-spacing: 0.05em;
}

.price-sheet-body {
  padding: 20px 18px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.plan-title-block {
  border-bottom: 1px solid var(--border-light);
  padding-bottom: 12px;
}

.plan-code-name {
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--text-main);
  letter-spacing: -0.01em;
}

.plan-sub-name {
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.plan-price-row {
  display: flex;
  align-items: baseline;
  gap: 4px;
}

.plan-currency {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text-main);
}

.plan-amount {
  font-size: 2rem;
  font-weight: 800;
  color: var(--text-main);
  line-height: 1;
}

.plan-period {
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.plan-traffic-badge {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 700;
  padding: 4px 8px;
  background: var(--bg-paper-gray);
  border-radius: var(--radius-sm);
  color: var(--text-main);
}

.price-sheet-focus .plan-traffic-badge {
  background: var(--doc-red-bg);
  color: var(--doc-red);
}

.plan-use-cases {
  font-size: 0.82rem;
  color: var(--text-body);
  line-height: 1.5;
  border-top: 1px solid var(--border-light);
  padding-top: 12px;
}

.plan-use-title {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  color: var(--text-secondary);
  margin-bottom: 4px;
  text-transform: uppercase;
}

.plan-cta-btn {
  margin-top: 10px;
  display: block;
  text-align: center;
  padding: 9px 12px;
  font-size: 0.85rem;
  font-weight: 600;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-sheet);
  background: var(--bg-paper);
  color: var(--text-main);
  transition: all 0.15s ease;
}

.plan-cta-btn:hover {
  background: var(--bg-paper-gray);
  border-color: var(--border-dark);
}

.price-sheet-focus .plan-cta-btn {
  background: var(--doc-red);
  color: #FFFDFC;
  border-color: var(--doc-red);
}

.price-sheet-focus .plan-cta-btn:hover {
  background: #ad3b28;
}

/* ==========================================================================
   SECTION 06: KNOWLEDGE ARCHIVE (BLOG) (DOCUMENT / 007)
   ========================================================================== */
.archive-list {
  display: flex;
  flex-direction: column;
  border-top: 1px solid var(--border-sheet);
}

.archive-entry {
  display: grid;
  grid-template-columns: 110px 1fr 180px;
  gap: 20px;
  align-items: center;
  padding: 18px 12px;
  border-bottom: 1px solid var(--border-light);
  transition: background-color 0.15s ease;
}

.archive-entry:hover {
  background-color: var(--bg-paper-subtle);
}

.archive-doc-id {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--doc-red);
}

.archive-main-info {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.archive-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-main);
  line-height: 1.35;
}

.archive-entry:hover .archive-title {
  color: var(--doc-red);
}

.archive-desc {
  font-size: 0.88rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

.archive-meta {
  text-align: right;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 6px;
}

.archive-cat-tag {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--steel-blue);
  background: var(--steel-blue-bg);
  padding: 2px 8px;
  border-radius: var(--radius-sm);
}

.archive-read-link {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-main);
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

/* ==========================================================================
   SECTION 07: FIELD NOTES (DOCUMENT / 008)
   ========================================================================== */
.field-notes-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}

.field-note-card {
  background: var(--bg-paper);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.note-tab {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--muted-olive);
  letter-spacing: 0.08em;
}

.note-topic {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-main);
}

.note-quote {
  font-size: 0.9rem;
  color: var(--text-body);
  line-height: 1.6;
  font-style: normal;
}

/* ==========================================================================
   SECTION 08: REFERENCE SHEET (FAQ) (DOCUMENT / 009)
   ========================================================================== */
.faq-reference-list {
  border-top: 1px solid var(--border-sheet);
}

.faq-item {
  border-bottom: 1px solid var(--border-light);
}

.faq-question-btn {
  width: 100%;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 16px 10px;
  background: transparent;
  border: none;
  text-align: left;
  font-family: inherit;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-main);
  cursor: pointer;
  transition: color 0.15s ease;
}

.faq-question-btn:hover {
  color: var(--doc-red);
}

.faq-q-left {
  display: flex;
  align-items: center;
  gap: 16px;
}

.faq-ref-id {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--steel-blue);
}

.faq-icon {
  font-family: var(--font-mono);
  font-size: 1.2rem;
  font-weight: 400;
  color: var(--text-secondary);
  transition: transform 0.2s ease;
}

.faq-answer-panel {
  display: none;
  padding: 0 10px 18px 52px;
  font-size: 0.92rem;
  color: var(--text-body);
  line-height: 1.65;
}

.faq-item.is-open .faq-answer-panel {
  display: block;
}

.faq-item.is-open .faq-icon {
  transform: rotate(45deg);
}

/* ==========================================================================
   FOOTER: DOCUMENT END MATTER (Sections 108-115)
   ========================================================================== */
.document-end-matter {
  background-color: var(--bg-footer);
  border-top: 1px solid var(--border-sheet);
  padding: 40px 0 24px 0;
  color: var(--text-body);
  font-size: 0.88rem;
}

.footer-top-strip {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--border-sheet);
  margin-bottom: 28px;
  flex-wrap: wrap;
  gap: 16px;
}

.footer-brand-title {
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--text-main);
  letter-spacing: -0.01em;
}

.footer-brand-sub {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-secondary);
  letter-spacing: 0.08em;
}

.footer-columns-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;
  margin-bottom: 30px;
}

.footer-col-title {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--text-main);
  letter-spacing: 0.08em;
  margin-bottom: 12px;
  text-transform: uppercase;
}

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

.footer-link-list a {
  color: var(--text-body);
  font-size: 0.85rem;
}

.footer-link-list a:hover {
  color: var(--doc-red);
}

.footer-bottom-strip {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 20px;
  border-top: 1px solid var(--border-light);
  font-size: 0.78rem;
  color: var(--text-secondary);
  flex-wrap: wrap;
  gap: 12px;
}

.footer-legal-links {
  display: flex;
  gap: 16px;
}

.footer-legal-links a:hover {
  color: var(--text-main);
}

/* ==========================================================================
   DOCUMENT READER STYLES (Article Pages & Category Pages)
   ========================================================================== */
.doc-reader-container {
  max-width: 820px;
  margin: 30px auto 60px auto;
  padding-left: 20px;
  padding-right: 20px;
}

.doc-reader-sheet {
  background: var(--bg-sheet);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  box-shadow: var(--shadow-sheet);
  padding: 44px 50px;
}

.doc-breadcrumbs {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-secondary);
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 6px;
  flex-wrap: wrap;
}

.doc-breadcrumbs a:hover {
  color: var(--doc-red);
}

.doc-header {
  border-bottom: 1px solid var(--border-sheet);
  padding-bottom: 24px;
  margin-bottom: 30px;
}

.doc-id-badge {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--doc-red);
  background: var(--doc-red-bg);
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  margin-bottom: 12px;
}

.doc-article-title {
  font-size: clamp(1.8rem, 3.2vw, 2.45rem);
  font-weight: 800;
  color: var(--text-main);
  line-height: 1.25;
  letter-spacing: -0.015em;
  margin-bottom: 14px;
}

.doc-lead {
  font-size: 1.05rem;
  line-height: 1.65;
  color: var(--text-body);
  margin-bottom: 18px;
}

.doc-meta-strip {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-secondary);
  padding-top: 12px;
  border-top: 1px solid var(--border-light);
}

/* Executive Summary (GEO Quick Answer Box) */
.quick-answer {
  background: var(--bg-paper);
  border: 1px solid var(--border-sheet);
  border-left: 4px solid var(--doc-red);
  border-radius: 0 var(--radius-sheet) var(--radius-sheet) 0;
  padding: 24px;
  margin-bottom: 36px;
}

.quick-answer-tag {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--doc-red);
  letter-spacing: 0.08em;
  display: block;
  margin-bottom: 6px;
}

.quick-answer h2 {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 10px;
}

.quick-answer p {
  font-size: 0.95rem;
  line-height: 1.65;
  color: var(--text-body);
  margin-bottom: 0;
}

/* Document Table of Contents */
.doc-toc {
  background: var(--bg-paper-subtle);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sheet);
  padding: 20px 24px;
  margin-bottom: 36px;
}

.doc-toc-title {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--text-main);
  letter-spacing: 0.06em;
  margin-bottom: 12px;
  text-transform: uppercase;
}

.doc-toc-list {
  list-style: none;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px 20px;
}

.doc-toc-list a {
  font-size: 0.88rem;
  color: var(--steel-blue);
  display: inline-flex;
  align-items: baseline;
  gap: 6px;
}

.doc-toc-list a:hover {
  color: var(--doc-red);
}

.toc-num {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-secondary);
}

/* Markdown / Article Content Typography */
.doc-body {
  font-size: 1rem;
  line-height: 1.8;
  color: var(--text-body);
}

.doc-body h2 {
  font-size: 1.45rem;
  font-weight: 700;
  color: var(--text-main);
  margin-top: 40px;
  margin-bottom: 16px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border-light);
}

.doc-body h3 {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text-main);
  margin-top: 28px;
  margin-bottom: 12px;
}

.doc-body p {
  margin-bottom: 1.25rem;
}

.doc-body ul, .doc-body ol {
  margin-bottom: 1.25rem;
  padding-left: 24px;
}

.doc-body li {
  margin-bottom: 0.5rem;
}

.doc-body table {
  width: 100%;
  border-collapse: collapse;
  margin: 28px 0;
  font-size: 0.88rem;
}

.doc-body th, .doc-body td {
  border: 1px solid var(--border-sheet);
  padding: 10px 14px;
  text-align: left;
}

.doc-body th {
  background-color: var(--bg-paper);
  font-weight: 700;
  color: var(--text-main);
}

.doc-body tr:nth-child(even) {
  background-color: var(--bg-paper-subtle);
}

/* In-article Commercial Sheet Banner */
.doc-cta-sheet {
  background: var(--bg-paper);
  border: 1px solid var(--border-sheet);
  border-radius: var(--radius-sheet);
  padding: 24px;
  margin: 36px 0;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 16px;
}

.doc-cta-left h4 {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 4px;
}

.doc-cta-left p {
  font-size: 0.88rem;
  color: var(--text-secondary);
  margin: 0;
}

/* ==========================================================================
   RESPONSIVE DESIGN (375px, 390px, 430px, 768px, 1024px, 1440px)
   ========================================================================== */
@media (max-width: 1024px) {
  .hero-specs-grid {
    grid-template-columns: 1fr 1fr;
    gap: 20px;
  }
  .hero-spec-col {
    border-right: none;
    border-bottom: 1px solid var(--border-light);
    padding-bottom: 12px;
  }
  .hero-spec-col:nth-last-child(-n+2) {
    border-bottom: none;
    padding-bottom: 0;
  }
  .pricing-stack {
    grid-template-columns: repeat(2, 1fr);
  }
  .price-sheet-focus {
    transform: none;
  }
}

@media (max-width: 768px) {
  /* Cancel horizontal sheet offsets on mobile (Sections 16 & 137) */
  .sheet-offset-1, .sheet-offset-2, .sheet-offset-3, .sheet-offset-4, .sheet-offset-5 {
    margin-left: 0 !important;
    max-width: 100% !important;
  }

  .sheet-content {
    padding: 24px 20px;
  }

  /* Header compact */
  .bar-center {
    display: none;
  }
  .bar-actions .btn-cta {
    display: none; /* Accessible inside index drawer */
  }

  /* Hero adjustments */
  .hero-stack-container {
    padding-top: 36px;
  }
  .tab-level-3 {
    left: 12px;
    right: 12px;
    height: 36px;
  }
  .tab-level-2 {
    top: 18px;
    left: 6px;
    right: 6px;
    height: 36px;
  }
  .hero-content {
    padding: 24px 20px;
  }
  .hero-main-title {
    font-size: 1.85rem;
  }
  .hero-tagline {
    font-size: 1.6rem;
  }
  .hero-specs-grid {
    grid-template-columns: 1fr;
  }
  .hero-spec-col {
    border-bottom: 1px solid var(--border-light);
    padding-bottom: 10px;
  }
  .hero-spec-col:last-child {
    border-bottom: none;
  }

  /* Global section single column */
  .global-sheet-grid {
    grid-template-columns: 1fr;
    gap: 24px;
  }
  .global-sheet-grid::after {
    display: none;
  }

  /* Device section */
  .device-spec-row {
    grid-template-columns: 40px 1fr 90px;
    gap: 8px;
  }
  .device-desc {
    grid-column: 2 / span 2;
    margin-top: 4px;
  }
  .device-action {
    grid-column: 2 / span 2;
    text-align: left;
    margin-top: 6px;
  }

  /* AI & Media */
  .ai-sheet-grid {
    grid-template-columns: 1fr;
  }
  .ai-tools-list {
    grid-template-columns: 1fr 1fr;
  }
  .media-names {
    gap: 16px;
  }
  .media-item {
    font-size: 1.15rem;
  }

  /* Pricing vertical stack */
  .pricing-stack {
    grid-template-columns: 1fr;
  }

  /* Knowledge archive mobile (Section 142) */
  .archive-entry {
    grid-template-columns: 1fr;
    gap: 8px;
    padding: 16px 8px;
  }
  .archive-meta {
    flex-direction: row;
    justify-content: space-between;
    width: 100%;
    margin-top: 6px;
  }

  /* Field notes mobile */
  .field-notes-grid {
    grid-template-columns: 1fr;
  }

  /* FAQ mobile */
  .faq-q-left {
    gap: 10px;
  }
  .faq-answer-panel {
    padding-left: 20px;
  }

  /* Footer */
  .footer-columns-grid {
    grid-template-columns: 1fr 1fr;
    gap: 20px;
  }

  /* Document reader */
  .doc-reader-sheet {
    padding: 24px 18px;
  }
  .doc-toc-list {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 430px) {
  .hero-main-title {
    font-size: 1.65rem;
  }
  .hero-tagline {
    font-size: 1.45rem;
  }
  .footer-columns-grid {
    grid-template-columns: 1fr;
  }
  .ai-tools-list {
    grid-template-columns: 1fr;
  }
}

/* Accessibility: Prefers Reduced Motion (Section 135) */
@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;
  }
}