/* ─── S-Core Dream Font ─────────────────────────────────── */
@font-face {
  font-family: 'S-CoreDream';
  font-weight: 300;
  font-display: swap;
  src: url('https://cdn.jsdelivr.net/gh/projectnoonnu/noonfonts_six@1.2/S-CoreDream-3Light.woff') format('woff');
}
@font-face {
  font-family: 'S-CoreDream';
  font-weight: 400;
  font-display: swap;
  src: url('https://cdn.jsdelivr.net/gh/projectnoonnu/noonfonts_six@1.2/S-CoreDream-4Regular.woff') format('woff');
}
@font-face {
  font-family: 'S-CoreDream';
  font-weight: 500;
  font-display: swap;
  src: url('https://cdn.jsdelivr.net/gh/projectnoonnu/noonfonts_six@1.2/S-CoreDream-5Medium.woff') format('woff');
}
@font-face {
  font-family: 'S-CoreDream';
  font-weight: 600;
  font-display: swap;
  src: url('https://cdn.jsdelivr.net/gh/projectnoonnu/noonfonts_six@1.2/S-CoreDream-6Bold.woff') format('woff');
}
@font-face {
  font-family: 'S-CoreDream';
  font-weight: 700;
  font-display: swap;
  src: url('https://cdn.jsdelivr.net/gh/projectnoonnu/noonfonts_six@1.2/S-CoreDream-7ExtraBold.woff') format('woff');
}
@font-face {
  font-family: 'S-CoreDream';
  font-weight: 800;
  font-display: swap;
  src: url('https://cdn.jsdelivr.net/gh/projectnoonnu/noonfonts_six@1.2/S-CoreDream-8Heavy.woff') format('woff');
}

/* ─── Design Tokens ─────────────────────────────────────── */
:root {
  --font: 'S-CoreDream', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;

  /* Brand */
  --primary:       #0066FF;
  --primary-hover: #0054D1;
  --accent:        #FF5E00;
  --success:       #00BF40;
  --warning:       #FF9200;
  --danger:        #E52222;

  /* Surface */
  --bg:            #FFFDF9;
  --surface:       #FFFFFF;
  --surface-2:     #F7F6F2;
  --border:        rgba(112,115,124,0.18);
  --border-hover:  rgba(112,115,124,0.38);

  /* Text */
  --text-1: #171719;
  --text-2: rgba(46,47,51,0.88);
  --text-3: rgba(55,56,60,0.61);
  --text-4: rgba(55,56,60,0.38);

  /* Shadows */
  --shadow-sm: 0 1px 4px rgba(0,0,0,0.07), 0 0 1px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.09), 0 0 1px rgba(0,0,0,0.06);
  --shadow-lg: 0 12px 32px rgba(0,0,0,0.11), 0 0 1px rgba(0,0,0,0.07);

  /* Category — 사전·기초 */
  --cat-basics-h:    #4F6BEF;
  --cat-basics-bg:   #EEF2FF;
  --cat-basics-text: #2B4AC8;
  --cat-basics-soft: rgba(79,107,239,0.10);

  /* Category — 핵심 서비스 */
  --cat-core-h:    #FF6B2B;
  --cat-core-bg:   #FFF0E8;
  --cat-core-text: #C03A00;
  --cat-core-soft: rgba(255,107,43,0.10);

  /* Category — 운영·자동화 */
  --cat-ops-h:    #12B886;
  --cat-ops-bg:   #E6FAF5;
  --cat-ops-text: #0A7557;
  --cat-ops-soft: rgba(18,184,134,0.10);

  /* Category — 실전·심화 */
  --cat-adv-h:    #F03E3E;
  --cat-adv-bg:   #FFF5F5;
  --cat-adv-text: #C92A2A;
  --cat-adv-soft: rgba(240,62,62,0.10);

  /* Layout */
  --max-w:    1200px;
  --content-w: 780px;
  --gutter:   24px;

  /* Radii */
  --r-xs: 6px;
  --r-sm: 10px;
  --r-md: 16px;
  --r-lg: 24px;
  --r-full: 9999px;
}

/* ─── Reset & Base ──────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text-1);
  font-size: 16px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-wrap: pretty;
}
a { color: inherit; text-decoration: none; }
img { display: block; max-width: 100%; }
table { border-collapse: collapse; width: 100%; }

/* ─── Layout ────────────────────────────────────────────── */
.container {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 var(--gutter);
}
.content-container {
  max-width: var(--content-w);
  margin: 0 auto;
  padding: 0 var(--gutter);
}

/* ─── Site Header ───────────────────────────────────────── */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,253,249,0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  height: 60px;
}
.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 16px;
  color: var(--text-1);
  flex-shrink: 0;
}
.logo-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  background: var(--primary);
  color: #fff;
  border-radius: var(--r-sm);
  font-size: 17px;
}
.logo-text { font-weight: 700; }
.logo-sub {
  font-size: 12px;
  font-weight: 400;
  color: var(--text-3);
  margin-left: 4px;
}

/* Header progress */
.header-progress {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 13px;
  color: var(--text-3);
}
.header-prog-bar {
  width: 100px;
  height: 6px;
  background: var(--border);
  border-radius: var(--r-full);
  overflow: hidden;
}
.header-prog-fill {
  height: 100%;
  background: var(--primary);
  border-radius: var(--r-full);
  transition: width 0.4s ease;
}
.header-prog-label {
  font-weight: 600;
  color: var(--text-2);
  white-space: nowrap;
}

/* Mobile menu toggle */
.nav-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border: none;
  background: none;
  cursor: pointer;
  color: var(--text-1);
  border-radius: var(--r-sm);
}
.nav-toggle:hover { background: var(--surface-2); }

/* ─── Hero ──────────────────────────────────────────────── */
.hero {
  padding: 64px 0 56px;
  border-bottom: 1px solid var(--border);
}
.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 14px;
  background: rgba(0,102,255,0.08);
  color: var(--primary);
  border-radius: var(--r-full);
  font-size: 12px;
  font-weight: 600;
  margin-bottom: 20px;
}
.hero-title {
  font-size: clamp(26px, 4vw, 40px);
  font-weight: 800;
  line-height: 1.25;
  letter-spacing: -0.02em;
  color: var(--text-1);
  margin-bottom: 12px;
}
.hero-desc {
  font-size: 16px;
  color: var(--text-3);
  line-height: 1.75;
  max-width: 560px;
  margin-bottom: 36px;
}

/* Stats */
.stats-row {
  display: flex;
  gap: 0;
  flex-wrap: wrap;
  margin-bottom: 36px;
}
.stat {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  padding: 16px 28px 16px 0;
  border-right: 1px solid var(--border);
  margin-right: 28px;
}
.stat:last-child { border-right: none; }
.stat-num {
  font-size: 32px;
  font-weight: 800;
  color: var(--primary);
  line-height: 1;
  margin-bottom: 4px;
}
.stat-label {
  font-size: 12px;
  color: var(--text-3);
  font-weight: 500;
}

/* Progress block */
.progress-block {
  max-width: 480px;
}
.progress-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  margin-bottom: 10px;
}
.progress-title-text {
  font-size: 13px;
  font-weight: 600;
  color: var(--text-2);
}
.progress-label {
  font-size: 13px;
  font-weight: 600;
  color: var(--primary);
}
.progress-track {
  width: 100%;
  height: 8px;
  background: var(--border);
  border-radius: var(--r-full);
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary) 0%, #3B82F6 100%);
  border-radius: var(--r-full);
  transition: width 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ─── Course Navigation Tabs ────────────────────────────── */
.course-nav {
  display: flex;
  gap: 4px;
  padding: 20px 0 0;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
}
.course-nav::-webkit-scrollbar { display: none; }
.course-tab {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 18px;
  border-radius: var(--r-full);
  font-size: 13px;
  font-weight: 600;
  white-space: nowrap;
  cursor: pointer;
  border: 1.5px solid transparent;
  transition: background 0.15s, border-color 0.15s, color 0.15s;
  color: var(--text-3);
  background: none;
}
.course-tab:hover { background: var(--surface-2); color: var(--text-2); }
.course-tab.active-basics { background: var(--cat-basics-bg); color: var(--cat-basics-text); border-color: var(--cat-basics-text); }
.course-tab.active-core   { background: var(--cat-core-bg);   color: var(--cat-core-text);   border-color: var(--cat-core-text); }
.course-tab.active-ops    { background: var(--cat-ops-bg);    color: var(--cat-ops-text);    border-color: var(--cat-ops-text); }
.course-tab.active-adv    { background: var(--cat-adv-bg);    color: var(--cat-adv-text);    border-color: var(--cat-adv-text); }
.tab-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  display: inline-block;
}

/* ─── Main Content ──────────────────────────────────────── */
.main-content { padding: 56px 0 80px; }

/* Category Section */
.category-section { margin-bottom: 56px; }
.category-header {
  display: flex;
  align-items: baseline;
  gap: 12px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}
.category-badge {
  display: inline-flex;
  align-items: center;
  padding: 4px 12px;
  border-radius: var(--r-full);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.02em;
}
.cat-badge-basics { background: var(--cat-basics-bg); color: var(--cat-basics-text); }
.cat-badge-core   { background: var(--cat-core-bg);   color: var(--cat-core-text); }
.cat-badge-ops    { background: var(--cat-ops-bg);    color: var(--cat-ops-text); }
.cat-badge-adv    { background: var(--cat-adv-bg);    color: var(--cat-adv-text); }

.category-range {
  font-size: 20px;
  font-weight: 700;
  color: var(--text-1);
}
.category-desc {
  font-size: 13px;
  color: var(--text-3);
}

/* ─── Chapter Grid ──────────────────────────────────────── */
.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
}

/* ─── Chapter Card ──────────────────────────────────────── */
.chapter-card {
  display: flex;
  flex-direction: column;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: transform 0.18s ease, box-shadow 0.18s ease, border-color 0.18s ease;
  cursor: pointer;
}
.chapter-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  border-color: var(--border-hover);
}

/* Card colored header */
.card-header {
  position: relative;
  padding: 20px 24px 16px;
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
}
.card-header-basics  { background: var(--cat-basics-h); }
.card-header-core    { background: var(--cat-core-h); }
.card-header-ops     { background: var(--cat-ops-h); }
.card-header-adv     { background: var(--cat-adv-h); }

.chapter-num-display {
  font-size: 42px;
  font-weight: 800;
  color: rgba(255,255,255,0.9);
  line-height: 1;
  letter-spacing: -0.03em;
}
.chapter-prefix {
  font-size: 11px;
  font-weight: 600;
  color: rgba(255,255,255,0.65);
  letter-spacing: 0.06em;
  margin-bottom: 2px;
}
.chapter-check-badge {
  display: none;
  align-items: center;
  justify-content: center;
  width: 26px;
  height: 26px;
  background: rgba(255,255,255,0.25);
  border-radius: 50%;
  color: #fff;
  font-size: 13px;
  font-weight: 700;
  flex-shrink: 0;
}
.chapter-card.is-completed .chapter-check-badge { display: flex; }

/* Card body */
.card-body {
  flex: 1;
  padding: 18px 20px 14px;
}
.card-tags {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin-bottom: 12px;
}
.card-title {
  font-size: 18px;
  font-weight: 700;
  color: var(--text-1);
  margin-bottom: 2px;
  line-height: 1.3;
}
.card-subtitle {
  font-size: 13px;
  font-weight: 500;
  color: var(--text-3);
  margin-bottom: 10px;
}
.card-services {
  font-size: 12px;
  color: var(--text-4);
  line-height: 1.6;
}

/* Card footer */
.card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 20px;
  border-top: 1px solid var(--border);
  background: var(--surface-2);
}
.card-meta {
  font-size: 12px;
  font-weight: 500;
  color: var(--text-3);
}
.card-arrow {
  font-size: 16px;
  color: var(--text-3);
  transition: transform 0.15s, color 0.15s;
}
.chapter-card:hover .card-arrow {
  transform: translateX(4px);
  color: var(--primary);
}

/* Completed state */
.chapter-card.is-completed { border-color: rgba(0,191,64,0.3); }
.chapter-card.is-completed .card-footer { background: rgba(0,191,64,0.05); }

/* ─── Tags ──────────────────────────────────────────────── */
.tag {
  display: inline-flex;
  align-items: center;
  gap: 3px;
  padding: 3px 9px;
  border-radius: var(--r-full);
  font-size: 11px;
  font-weight: 600;
  white-space: nowrap;
  line-height: 1;
}
.tag-free    { background: #EBFBEE; color: #087F3E; }
.tag-billing { background: #FFF9DB; color: #916B00; }
.tag-danger  { background: #FFF5F5; color: #C92A2A; }
.tag-info    { background: #EEF2FF; color: #3451B2; }
.tag-neutral { background: #F1F3F5; color: #495057; }
.tag-cat-basics { background: var(--cat-basics-bg); color: var(--cat-basics-text); }
.tag-cat-core   { background: var(--cat-core-bg);   color: var(--cat-core-text); }
.tag-cat-ops    { background: var(--cat-ops-bg);    color: var(--cat-ops-text); }
.tag-cat-adv    { background: var(--cat-adv-bg);    color: var(--cat-adv-text); }

/* ─── Site Footer ───────────────────────────────────────── */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 32px 0;
  background: var(--surface-2);
}
.site-footer p {
  font-size: 13px;
  color: var(--text-4);
  text-align: center;
  line-height: 1.7;
}

/* ═══════════════════════════════════════════════════════════
   CHAPTER PAGE STYLES
═══════════════════════════════════════════════════════════ */

/* Chapter top nav */
.chapter-topnav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,253,249,0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.chapter-topnav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 56px;
  gap: 16px;
}
.back-link {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 14px;
  font-weight: 500;
  color: var(--text-3);
  transition: color 0.15s;
}
.back-link:hover { color: var(--primary); }
.back-arrow { font-size: 16px; }
.chapter-nav-label {
  font-size: 13px;
  font-weight: 600;
  color: var(--text-2);
}
.chapter-nav-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}
.complete-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 7px 16px;
  border-radius: var(--r-full);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  border: 1.5px solid var(--border-hover);
  background: var(--surface);
  color: var(--text-2);
  font-family: var(--font);
  transition: all 0.15s;
}
.complete-btn:hover { border-color: var(--success); color: var(--success); }
.complete-btn.is-completed {
  background: #EBFBEE;
  border-color: transparent;
  color: #087F3E;
}

/* Chapter hero */
.chapter-hero {
  padding: 56px 0 48px;
  border-bottom: 1px solid var(--border);
}
.chapter-hero-inner {
  display: grid;
  grid-template-columns: 1fr 280px;
  gap: 48px;
  align-items: start;
}
.chapter-hero-left {}
.chapter-hero-number {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.1em;
  color: var(--text-4);
  text-transform: uppercase;
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.chapter-num-badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: var(--r-sm);
  font-size: 18px;
  font-weight: 800;
  color: #fff;
}
.chapter-hero-title {
  font-size: clamp(24px, 3.5vw, 36px);
  font-weight: 800;
  line-height: 1.2;
  letter-spacing: -0.02em;
  color: var(--text-1);
  margin-bottom: 8px;
}
.chapter-hero-subtitle {
  font-size: 18px;
  font-weight: 400;
  color: var(--text-3);
  margin-bottom: 20px;
}
.chapter-hero-tags {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 24px;
}
.chapter-hero-services {
  font-size: 14px;
  color: var(--text-3);
  line-height: 1.7;
}

/* Chapter info card */
.chapter-info-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  padding: 24px;
  box-shadow: var(--shadow-sm);
}
.info-card-title {
  font-size: 13px;
  font-weight: 700;
  color: var(--text-3);
  margin-bottom: 16px;
  letter-spacing: 0.04em;
}
.info-card-item {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  font-size: 14px;
  color: var(--text-2);
  padding: 8px 0;
  border-bottom: 1px solid var(--border);
  line-height: 1.5;
}
.info-card-item:last-child { border-bottom: none; }
.info-icon {
  font-size: 16px;
  flex-shrink: 0;
  margin-top: 1px;
}

/* Chapter layout with sidebar TOC */
.chapter-layout {
  display: grid;
  grid-template-columns: 1fr 240px;
  gap: 48px;
  align-items: start;
  padding: 48px 0 80px;
}
.chapter-content {}

/* Sticky TOC */
.chapter-toc {
  position: sticky;
  top: 76px;
}
.toc-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  padding: 20px;
  box-shadow: var(--shadow-sm);
}
.toc-title {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.08em;
  color: var(--text-4);
  text-transform: uppercase;
  margin-bottom: 12px;
}
.toc-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.toc-link {
  display: block;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-3);
  padding: 6px 10px;
  border-radius: var(--r-xs);
  transition: color 0.12s, background 0.12s;
  line-height: 1.45;
}
.toc-link:hover { color: var(--text-1); background: var(--surface-2); }
.toc-link.is-active { color: var(--primary); background: rgba(0,102,255,0.07); font-weight: 600; }
.toc-link-h3 { padding-left: 22px; font-size: 12px; }

/* Content styles */
.content-section {
  margin-bottom: 56px;
  scroll-margin-top: 80px;
}
.section-label {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.08em;
  color: var(--text-4);
  text-transform: uppercase;
  margin-bottom: 10px;
}
.content-section h2 {
  font-size: 24px;
  font-weight: 700;
  color: var(--text-1);
  margin-bottom: 20px;
  letter-spacing: -0.015em;
  line-height: 1.3;
}
.content-section h3 {
  font-size: 18px;
  font-weight: 700;
  color: var(--text-1);
  margin: 32px 0 14px;
  letter-spacing: -0.01em;
}
.content-section p {
  font-size: 15px;
  color: var(--text-2);
  line-height: 1.8;
  margin-bottom: 16px;
}
.content-section strong { color: var(--text-1); font-weight: 700; }
.content-section code {
  font-family: 'Fira Code', 'Cascadia Code', 'SF Mono', monospace;
  font-size: 13px;
  background: var(--surface-2);
  color: #C03A00;
  padding: 2px 6px;
  border-radius: 4px;
  border: 1px solid var(--border);
}

/* Callout */
.callout {
  display: flex;
  gap: 12px;
  padding: 16px 20px;
  border-radius: var(--r-md);
  margin: 20px 0;
  font-size: 14px;
  line-height: 1.7;
}
.callout-tip   { background: rgba(0,102,255,0.06); border-left: 3px solid var(--primary); }
.callout-warn  { background: rgba(255,146,0,0.07); border-left: 3px solid var(--warning); }
.callout-danger { background: rgba(229,34,34,0.06); border-left: 3px solid var(--danger); }
.callout-icon { font-size: 18px; flex-shrink: 0; margin-top: 1px; }
.callout-body { color: var(--text-2); }
.callout-body strong { color: var(--text-1); }

/* Diagram card */
.diagram-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  overflow: hidden;
  margin: 24px 0;
  box-shadow: var(--shadow-sm);
}
.diagram-header {
  padding: 12px 20px;
  background: var(--surface-2);
  border-bottom: 1px solid var(--border);
  font-size: 12px;
  font-weight: 600;
  color: var(--text-3);
}
.diagram-body { padding: 24px 20px; }

/* OSI Layer diagram */
.osi-layers { display: flex; flex-direction: column; gap: 4px; }
.osi-layer {
  display: grid;
  grid-template-columns: 32px 180px 1fr 100px;
  gap: 12px;
  align-items: center;
  padding: 10px 12px;
  border-radius: var(--r-xs);
  font-size: 13px;
}
.osi-num {
  font-size: 11px;
  font-weight: 800;
  color: rgba(255,255,255,0.9);
  text-align: center;
}
.osi-name { font-weight: 700; color: rgba(255,255,255,0.95); }
.osi-proto { color: rgba(255,255,255,0.75); font-size: 12px; }
.osi-aws {
  font-size: 11px;
  color: rgba(255,255,255,0.65);
  text-align: right;
}
.osi-l7 { background: #4F6BEF; }
.osi-l6 { background: #6C8EFF; }
.osi-l5 { background: #8AA5FF; }
.osi-l4 { background: #12B886; }
.osi-l3 { background: #20C997; }
.osi-l2 { background: #51CF9E; }
.osi-l1 { background: #87E0B8; }

/* DNS flow */
.dns-flow {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: center;
  padding: 16px 0;
}
.dns-node {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
  font-size: 12px;
  color: var(--text-2);
  font-weight: 500;
}
.dns-node-icon {
  width: 48px;
  height: 48px;
  border-radius: 12px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
}
.dns-arrow {
  font-size: 18px;
  color: var(--text-4);
  font-weight: 300;
}

/* Tables */
.content-table-wrap {
  overflow-x: auto;
  margin: 20px 0;
  border-radius: var(--r-md);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
}
.content-table {
  width: 100%;
  font-size: 14px;
}
.content-table th {
  background: var(--surface-2);
  font-size: 12px;
  font-weight: 700;
  color: var(--text-3);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 10px 16px;
  text-align: left;
  border-bottom: 1px solid var(--border);
}
.content-table td {
  padding: 12px 16px;
  color: var(--text-2);
  border-bottom: 1px solid var(--border);
  vertical-align: top;
  line-height: 1.6;
}
.content-table tr:last-child td { border-bottom: none; }
.content-table tr:hover td { background: rgba(0,0,0,0.018); }

/* Summary card */
.summary-card {
  background: rgba(0,102,255,0.04);
  border: 1px solid rgba(0,102,255,0.12);
  border-radius: var(--r-lg);
  padding: 28px 32px;
  margin: 40px 0;
}
.summary-card-title {
  font-size: 14px;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 8px;
}
.summary-item {
  display: flex;
  gap: 10px;
  align-items: baseline;
  padding: 6px 0;
  font-size: 14px;
  color: var(--text-2);
  border-bottom: 1px solid rgba(0,102,255,0.08);
}
.summary-item:last-child { border-bottom: none; }
.summary-term { font-weight: 600; color: var(--text-1); min-width: 120px; flex-shrink: 0; }

/* Prev/Next Nav */
.chapter-pagination {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-top: 56px;
  padding-top: 32px;
  border-top: 1px solid var(--border);
}
.pag-link {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 20px 24px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  transition: border-color 0.15s, box-shadow 0.15s;
  box-shadow: var(--shadow-sm);
}
.pag-link:hover { border-color: var(--primary); box-shadow: var(--shadow-md); }
.pag-link.pag-next { align-items: flex-end; text-align: right; }
.pag-dir {
  font-size: 11px;
  font-weight: 700;
  color: var(--text-4);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}
.pag-title {
  font-size: 15px;
  font-weight: 700;
  color: var(--text-1);
  line-height: 1.35;
}
.pag-sub { font-size: 12px; color: var(--text-3); }

/* ─── Responsive ────────────────────────────────────────── */
@media (max-width: 900px) {
  .chapter-hero-inner { grid-template-columns: 1fr; }
  .chapter-info-card { display: none; }
  .chapter-layout { grid-template-columns: 1fr; }
  .chapter-toc { display: none; }
}
@media (max-width: 640px) {
  :root { --gutter: 16px; }
  .hero { padding: 40px 0 36px; }
  .hero-badge { font-size: 11px; }
  .hero-desc { font-size: 15px; }
  .stats-row { gap: 0; }
  .stat { padding: 12px 20px 12px 0; margin-right: 20px; }
  .stat-num { font-size: 26px; }
  .header-progress { display: none; }
  .chapter-grid { grid-template-columns: 1fr; }
  .chapter-pagination { grid-template-columns: 1fr; }
  .osi-layer { grid-template-columns: 24px 1fr 1fr; }
  .osi-aws { display: none; }
  .chapter-hero-title { font-size: 22px; }
  .chapter-hero-subtitle { font-size: 15px; }
  .content-section h2 { font-size: 20px; }
  .content-section h3 { font-size: 16px; }
}