/* ========================================
   深入理解现代Web架构 - 羊皮纸编辑部风格
   ======================================== */

/* CSS Variables */
:root {
  --canvas: #faf9f5;
  --paper-light: #f5f2eb;
  --paper-dark: #e8e2d5;
  --ink-primary: #1a1a16;
  --ink-secondary: #4a4742;
  --ink-tertiary: #7a7670;
  --ink-placeholder: #b0aca5;
  --reverse-bg: #1a1a1a;
  --reverse-text: #f5f2eb;
  --accent: #d4a853;
  --accent-secondary: #2d2d28;
  --link: #7c5c3c;
  --success: #3a7d44;
  --warning: #c4744c;
  --max-width: 960px;
  --narrow-width: 640px;
  --radius: 24px;
  --radius-sm: 16px;
  --radius-xs: 12px;
  --radius-badge: 20px;
  --section-gap: 120px;
  --section-gap-sm: 80px;
}

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

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: 'Source Serif 4', 'Noto Serif SC', 'Merriweather', 'Lora', Georgia, serif;
  font-size: 15px;
  line-height: 1.7;
  color: var(--ink-primary);
  background-color: var(--canvas);
  max-width: 100%;
  overflow-x: hidden;
}

/* Reading Progress Bar */
.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  height: 2px;
  background: var(--accent);
  opacity: 0.8;
  z-index: 9999;
  transition: width 100ms linear;
  width: 0%;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-family: 'Source Serif 4', 'Noto Serif SC', 'Merriweather', Georgia, serif;
  color: var(--ink-primary);
  font-weight: 700;
}

.hero-title {
  font-size: 60px;
  line-height: 1.1;
  letter-spacing: -0.06em;
  font-weight: 700;
}

.display-title {
  font-size: 48px;
  line-height: 1.15;
  letter-spacing: -0.05em;
}

.heading-lg {
  font-size: 36px;
  line-height: 1.25;
  letter-spacing: -0.04em;
}

.heading {
  font-size: 28px;
  line-height: 1.35;
  letter-spacing: -0.03em;
}

.heading-sm {
  font-size: 20px;
  line-height: 1.4;
  letter-spacing: -0.02em;
}

.heading-xs {
  font-size: 16px;
  line-height: 1.5;
  letter-spacing: -0.01em;
  font-weight: 600;
}

.body-lg {
  font-size: 16px;
  line-height: 1.7;
  letter-spacing: -0.01em;
}

.quote-text {
  font-size: 18px;
  line-height: 1.65;
  font-style: italic;
}

.caption {
  font-size: 14px;
  line-height: 1.6;
}

.micro {
  font-size: 12px;
  line-height: 1.5;
  letter-spacing: 0.01em;
  font-family: 'Inter', 'DM Sans', 'Plus Jakarta Sans', system-ui, sans-serif;
}

.label {
  font-size: 13px;
  line-height: 1.4;
  letter-spacing: 0.02em;
  font-family: 'Inter', 'DM Sans', 'Plus Jakarta Sans', system-ui, sans-serif;
  font-weight: 500;
}

/* Underline emphasis */
.underline-accent {
  border-bottom: 3px solid var(--accent);
  padding-bottom: 4px;
  text-decoration: none;
}

.underline-secondary {
  border-bottom: 2px solid var(--accent-secondary);
  padding-bottom: 3px;
}

/* Links */
a {
  color: var(--link);
  text-decoration: none;
  transition: color 200ms ease, border-bottom-color 200ms ease;
}

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

.nav-link {
  font-family: 'Inter', 'DM Sans', system-ui, sans-serif;
  font-size: 14px;
  font-weight: 400;
  color: var(--ink-secondary);
  border-bottom: 1px solid transparent;
  padding-bottom: 2px;
  transition: color 200ms ease, border-bottom-color 200ms ease;
}

.nav-link:hover {
  color: var(--ink-primary);
  border-bottom-color: var(--accent);
}

/* Container */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

.container-narrow {
  max-width: var(--narrow-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* Navigation */
.site-nav {
  position: sticky;
  top: 0;
  background: var(--canvas);
  height: 64px;
  display: flex;
  align-items: center;
  border-bottom: 1px solid var(--paper-dark);
  z-index: 1000;
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-brand {
  display: flex;
  align-items: baseline;
  gap: 12px;
}

.nav-logo {
  font-family: 'Source Serif 4', 'Noto Serif SC', serif;
  font-size: 18px;
  font-weight: 600;
  color: var(--ink-primary);
}

.nav-course-name {
  font-family: 'Source Serif 4', 'Noto Serif SC', serif;
  font-size: 15px;
  font-weight: 400;
  color: var(--ink-secondary);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 24px;
}

.nav-mobile-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 8px;
}

.nav-mobile-toggle span {
  display: block;
  width: 20px;
  height: 2px;
  background: var(--ink-primary);
  margin: 4px 0;
  transition: transform 300ms ease;
}

/* Buttons */
.btn {
  display: inline-block;
  font-family: 'Inter', 'DM Sans', system-ui, sans-serif;
  font-size: 15px;
  font-weight: 500;
  border-radius: var(--radius);
  padding: 14px 32px;
  cursor: pointer;
  transition: all 250ms ease-out;
  text-align: center;
  text-decoration: none;
  border: none;
}

.btn-outline {
  background: transparent;
  color: var(--ink-primary);
  border: 2px solid var(--ink-primary);
}

.btn-outline:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.btn-dark {
  background: var(--reverse-bg);
  color: var(--reverse-text);
  border: none;
  width: 100%;
  padding: 16px 0;
  font-size: 16px;
  font-weight: 600;
  font-family: 'Source Serif 4', 'Noto Serif SC', serif;
}

.btn-dark:hover {
  background: var(--accent-secondary);
  transform: scale(1.01);
}

/* Section spacing */
.section {
  padding: var(--section-gap) 0;
}

.section-sm {
  padding: var(--section-gap-sm) 0;
}

/* Section label */
.section-label {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  font-weight: 500;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 16px;
}

/* Decorative line */
.deco-line {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 32px 0;
}

.deco-line::before,
.deco-line::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--paper-dark);
}

.deco-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--paper-dark);
}

/* Hero Section */
.hero {
  padding: 80px 0;
  text-align: center;
}

.hero .section-label {
  margin-bottom: 24px;
}

.hero-title {
  margin-bottom: 24px;
  max-width: 800px;
  margin-left: auto;
  margin-right: auto;
}

.hero-subtitle {
  font-size: 20px;
  line-height: 1.5;
  color: var(--ink-secondary);
  max-width: 560px;
  margin: 0 auto 40px;
  font-weight: 400;
}

.hero-cta {
  margin-top: 40px;
}

/* Course Outline - Two Column */
.outline-section {
  padding: var(--section-gap) 0;
}

.outline-grid {
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: 40px;
  align-items: start;
}

.outline-tree {
  position: sticky;
  top: 88px;
}

.tree-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 16px;
  border-radius: var(--radius);
  cursor: pointer;
  transition: background 200ms ease;
  border: none;
  background: none;
  width: 100%;
  text-align: left;
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 15px;
  color: var(--ink-primary);
}

.tree-item:hover {
  background: var(--paper-light);
}

.tree-item.active {
  background: var(--paper-light);
}

.tree-item-num {
  font-family: 'Source Serif 4', serif;
  font-size: 13px;
  font-weight: 600;
  color: var(--accent);
  min-width: 28px;
}

.tree-item-title {
  flex: 1;
}

.tree-item-duration {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 12px;
  color: var(--ink-tertiary);
}

.tree-children {
  max-height: 0;
  overflow: hidden;
  transition: max-height 350ms ease;
  padding-left: 16px;
  border-left: 1px solid var(--paper-dark);
  margin-left: 28px;
}

.tree-children.expanded {
  max-height: 500px;
}

.tree-child {
  padding: 8px 16px;
  font-size: 14px;
  color: var(--ink-secondary);
  cursor: pointer;
  border-radius: var(--radius);
  transition: background 200ms ease;
}

.tree-child:hover {
  background: var(--paper-light);
  color: var(--ink-primary);
}

.outline-preview {
  min-height: 300px;
}

.outline-preview-content {
  opacity: 1;
  transition: opacity 350ms ease, transform 350ms ease;
}

.outline-preview-content.fading {
  opacity: 0;
  transform: translateX(-8px);
}

.preview-title {
  font-size: 28px;
  margin-bottom: 16px;
}

.preview-desc {
  color: var(--ink-secondary);
  margin-bottom: 24px;
  max-width: 72ch;
}

.preview-objectives {
  list-style: none;
}

.preview-objectives li {
  padding: 8px 0;
  padding-left: 20px;
  position: relative;
  color: var(--ink-secondary);
}

.preview-objectives li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 16px;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--accent);
}

/* Preview Cards (Reverse) */
.preview-cards {
  display: flex;
  gap: 24px;
}

.preview-card {
  background: var(--reverse-bg);
  border-radius: var(--radius);
  padding: 40px;
  flex: 1;
  transition: transform 250ms ease-out, filter 250ms ease-out;
  cursor: pointer;
}

.preview-card:hover {
  transform: scale(1.02);
  filter: brightness(1.05);
}

.preview-card-icon {
  color: var(--accent);
  font-size: 48px;
  margin-bottom: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 64px;
  height: 64px;
  border: 2px solid var(--accent);
  border-radius: 50%;
}

.preview-card-title {
  font-size: 28px;
  color: var(--reverse-text);
  margin-bottom: 12px;
  font-weight: 600;
}

.preview-card-desc {
  font-size: 15px;
  color: var(--ink-placeholder);
  margin-bottom: 20px;
  line-height: 1.6;
}

.preview-card-duration {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 12px;
  color: var(--ink-tertiary);
  margin-bottom: 16px;
}

/* Audio Player */
.audio-player {
  display: flex;
  align-items: center;
  gap: 12px;
  background: rgba(255,255,255,0.05);
  border-radius: var(--radius-sm);
  padding: 12px 16px;
}

.play-btn {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: var(--accent);
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: transform 200ms ease;
}

.play-btn:hover {
  transform: scale(1.1);
}

.play-btn svg {
  width: 14px;
  height: 14px;
  fill: var(--reverse-bg);
  margin-left: 2px;
}

.play-btn.playing svg {
  margin-left: 0;
}

.progress-track {
  flex: 1;
  height: 4px;
  background: #2a2a2a;
  border-radius: 2px;
  position: relative;
  cursor: pointer;
}

.progress-fill {
  height: 100%;
  background: var(--accent);
  border-radius: 2px;
  width: 0%;
  transition: width 100ms linear;
}

.progress-time {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 11px;
  color: var(--ink-tertiary);
  min-width: 36px;
  text-align: right;
}

/* Instructor Section */
.instructor-section {
  padding: var(--section-gap) 0;
}

.instructor-header {
  margin-bottom: 48px;
}

.instructor-name {
  font-size: 28px;
  font-weight: 700;
  margin-bottom: 8px;
}

.instructor-role {
  color: var(--ink-secondary);
  font-size: 16px;
}

.instructor-timeline {
  position: relative;
  padding-left: 100px;
}

.instructor-timeline::before {
  content: '';
  position: absolute;
  left: 80px;
  top: 0;
  bottom: 0;
  width: 1px;
  background: var(--paper-dark);
}

.timeline-item {
  display: flex;
  align-items: flex-start;
  gap: 20px;
  margin-bottom: 20px;
  position: relative;
}

.timeline-year {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  color: var(--ink-tertiary);
  position: absolute;
  left: -100px;
  width: 80px;
  text-align: right;
  padding-top: 2px;
}

.timeline-dot {
  position: absolute;
  left: -24px;
  top: 6px;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent);
}

.timeline-content {
  font-size: 15px;
  color: var(--ink-primary);
  line-height: 1.6;
}

.timeline-content .underline-secondary {
  font-weight: 500;
}

/* Pricing Section */
.pricing-section {
  padding: var(--section-gap) 0;
}

.pricing-inner {
  max-width: var(--narrow-width);
  margin: 0 auto;
  text-align: center;
}

.pricing-deco {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  margin-bottom: 32px;
}

.pricing-deco-line {
  width: 40px;
  height: 1px;
  background: var(--accent);
}

.pricing-deco-diamond {
  width: 8px;
  height: 8px;
  background: var(--accent);
  transform: rotate(45deg);
}

.pricing-title {
  font-size: 36px;
  margin-bottom: 24px;
}

.pricing-desc {
  font-size: 16px;
  color: var(--ink-secondary);
  line-height: 1.7;
  margin-bottom: 40px;
  max-width: 72ch;
  margin-left: auto;
  margin-right: auto;
}

.pricing-plans {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  margin-bottom: 40px;
  text-align: left;
}

.pricing-plan {
  background: var(--paper-light);
  border-radius: var(--radius);
  padding: 32px;
  transition: transform 200ms ease;
}

.pricing-plan:hover {
  transform: translateY(-2px);
}

.pricing-plan.featured {
  background: var(--reverse-bg);
  color: var(--reverse-text);
}

.plan-name {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent);
  margin-bottom: 12px;
}

.plan-price {
  font-size: 36px;
  font-weight: 700;
  margin-bottom: 16px;
}

.plan-price span {
  font-size: 16px;
  font-weight: 400;
  color: var(--ink-tertiary);
}

.pricing-plan.featured .plan-price span {
  color: var(--ink-placeholder);
}

.plan-features {
  list-style: none;
}

.plan-features li {
  padding: 8px 0;
  font-size: 14px;
  color: var(--ink-secondary);
  display: flex;
  align-items: flex-start;
  gap: 8px;
}

.pricing-plan.featured .plan-features li {
  color: var(--ink-placeholder);
}

.plan-features li::before {
  content: '';
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--success);
  flex-shrink: 0;
  margin-top: 2px;
  position: relative;
}

.plan-features li::after {
  content: '';
  position: absolute;
}

.pricing-trust {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  color: var(--ink-tertiary);
  margin-top: 16px;
}

/* Testimonials */
.testimonials-section {
  padding: var(--section-gap) 0;
}

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

.testimonial-card {
  background: var(--paper-light);
  border-radius: var(--radius);
  padding: 28px;
}

.testimonial-quote-mark {
  font-size: 36px;
  font-weight: 600;
  color: var(--accent);
  line-height: 1;
  margin-bottom: 12px;
}

.testimonial-text {
  font-size: 18px;
  font-style: italic;
  line-height: 1.65;
  color: var(--ink-primary);
  margin-bottom: 20px;
}

.testimonial-divider {
  width: 60px;
  height: 1px;
  background: var(--paper-dark);
  margin-bottom: 16px;
}

.testimonial-author {
  font-size: 14px;
  font-weight: 600;
  color: var(--ink-primary);
}

.testimonial-role {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 12px;
  color: var(--ink-tertiary);
  margin-top: 4px;
}

/* FAQ Section */
.faq-section {
  padding: var(--section-gap) 0;
}

.faq-list {
  max-width: var(--max-width);
}

.faq-item {
  margin-bottom: 8px;
}

.faq-question {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 0;
  border-bottom: 1px solid var(--paper-dark);
  cursor: pointer;
  transition: border-bottom-color 300ms ease;
  background: none;
  border-top: none;
  border-left: none;
  border-right: none;
  width: 100%;
  text-align: left;
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 15px;
  font-weight: 500;
  color: var(--ink-primary);
}

.faq-question:hover {
  border-bottom-color: var(--accent);
}

.faq-item.active .faq-question {
  border-bottom-color: var(--accent);
}

.faq-icon {
  font-size: 20px;
  color: var(--ink-tertiary);
  transition: transform 300ms ease;
  flex-shrink: 0;
  margin-left: 16px;
}

.faq-item.active .faq-icon {
  transform: rotate(45deg);
  color: var(--accent);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 300ms ease, padding 300ms ease;
}

.faq-answer-inner {
  padding: 16px 0;
  font-size: 15px;
  color: var(--ink-secondary);
  line-height: 1.7;
  max-width: 72ch;
}

.faq-item.active .faq-answer {
  max-height: 300px;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--paper-dark);
  padding: 48px 0;
  margin-top: var(--section-gap);
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 40px;
}

.footer-brand {
  max-width: 300px;
}

.footer-brand-name {
  font-size: 18px;
  font-weight: 600;
  margin-bottom: 8px;
}

.footer-brand-desc {
  font-size: 14px;
  color: var(--ink-tertiary);
  line-height: 1.6;
}

.footer-links {
  display: flex;
  gap: 48px;
}

.footer-col-title {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--ink-tertiary);
  margin-bottom: 16px;
}

.footer-col a {
  display: block;
  font-size: 14px;
  color: var(--ink-secondary);
  margin-bottom: 10px;
  transition: color 200ms ease;
}

.footer-col a:hover {
  color: var(--ink-primary);
}

.footer-bottom {
  margin-top: 40px;
  padding-top: 24px;
  border-top: 1px solid var(--paper-dark);
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 12px;
  color: var(--ink-tertiary);
  text-align: center;
}

/* Page Header (for inner pages) */
.page-header {
  padding: 60px 0 40px;
  text-align: center;
  border-bottom: 1px solid var(--paper-dark);
}

.page-header .section-label {
  margin-bottom: 16px;
}

.page-title {
  font-size: 48px;
  margin-bottom: 16px;
}

.page-desc {
  font-size: 18px;
  color: var(--ink-secondary);
  max-width: 560px;
  margin: 0 auto;
}

/* Chapter Page */
.chapter-content {
  padding: 60px 0;
}

.chapter-meta {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 32px;
}

.chapter-num {
  font-family: 'Source Serif 4', serif;
  font-size: 13px;
  font-weight: 600;
  color: var(--accent);
  background: var(--paper-light);
  padding: 4px 12px;
  border-radius: var(--radius-badge);
}

.chapter-duration {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  color: var(--ink-tertiary);
}

.chapter-body {
  max-width: 72ch;
}

.chapter-body h2 {
  font-size: 28px;
  margin: 40px 0 16px;
}

.chapter-body h3 {
  font-size: 20px;
  margin: 32px 0 12px;
}

.chapter-body p {
  margin-bottom: 16px;
  color: var(--ink-secondary);
  max-width: 72ch;
}

.chapter-body ul {
  margin-bottom: 16px;
  padding-left: 20px;
}

.chapter-body ul li {
  margin-bottom: 8px;
  color: var(--ink-secondary);
}

.chapter-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 60px;
  padding-top: 32px;
  border-top: 1px solid var(--paper-dark);
}

.chapter-nav a {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 14px;
  color: var(--link);
  display: flex;
  align-items: center;
  gap: 8px;
}

.chapter-nav a:hover {
  color: var(--ink-primary);
}

/* Login/Register Page */
.auth-section {
  padding: 80px 0;
  display: flex;
  justify-content: center;
}

.auth-card {
  width: 100%;
  max-width: 420px;
  background: var(--paper-light);
  border-radius: var(--radius);
  padding: 48px 40px;
}

.auth-title {
  font-size: 28px;
  text-align: center;
  margin-bottom: 32px;
}

.form-group {
  margin-bottom: 20px;
}

.form-label {
  display: block;
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  font-weight: 500;
  color: var(--ink-secondary);
  margin-bottom: 8px;
}

.form-input {
  width: 100%;
  padding: 12px 16px;
  border: 1px solid var(--paper-dark);
  border-radius: var(--radius-xs);
  font-family: 'Source Serif 4', serif;
  font-size: 15px;
  color: var(--ink-primary);
  background: var(--canvas);
  transition: border-color 200ms ease;
}

.form-input:focus {
  outline: none;
  border-color: var(--accent);
}

.form-input::placeholder {
  color: var(--ink-placeholder);
}

.auth-footer {
  text-align: center;
  margin-top: 24px;
  font-size: 14px;
  color: var(--ink-tertiary);
}

.auth-footer a {
  color: var(--link);
  font-weight: 500;
}

/* Enroll Page */
.enroll-section {
  padding: 60px 0;
}

.enroll-summary {
  background: var(--paper-light);
  border-radius: var(--radius);
  padding: 32px;
  margin-bottom: 40px;
}

.enroll-course-title {
  font-size: 24px;
  margin-bottom: 8px;
}

.enroll-plan-name {
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 16px;
}

.enroll-price {
  font-size: 36px;
  font-weight: 700;
}

.enroll-form {
  max-width: 560px;
}

/* Mobile Select for Outline */
.outline-mobile-select {
  display: none;
  width: 100%;
  padding: 12px 16px;
  border: 1px solid var(--paper-dark);
  border-radius: var(--radius-xs);
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 15px;
  color: var(--ink-primary);
  background: var(--canvas);
  margin-bottom: 24px;
}

/* Responsive */
@media (max-width: 1023px) {
  .outline-grid {
    grid-template-columns: 240px 1fr;
    gap: 24px;
  }
  
  .preview-cards {
    flex-wrap: wrap;
  }
  
  .preview-card {
    flex: 1 1 calc(50% - 12px);
  }
  
  .testimonials-grid {
    grid-template-columns: repeat(2, 1fr);
  }
  
  .pricing-plans {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 767px) {
  :root {
    --section-gap: 80px;
    --section-gap-sm: 60px;
  }
  
  .hero-title {
    font-size: 36px;
  }
  
  .display-title {
    font-size: 32px;
  }
  
  .heading-lg {
    font-size: 28px;
  }
  
  .page-title {
    font-size: 32px;
  }
  
  .nav-links {
    display: none;
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--canvas);
    border-bottom: 1px solid var(--paper-dark);
    flex-direction: column;
    padding: 16px 24px;
    gap: 16px;
  }
  
  .nav-links.open {
    display: flex;
  }
  
  .nav-mobile-toggle {
    display: block;
  }
  
  .outline-grid {
    grid-template-columns: 1fr;
  }
  
  .outline-tree {
    display: none;
  }
  
  .outline-mobile-select {
    display: block;
  }
  
  .preview-cards {
    flex-direction: column;
  }
  
  .preview-card {
    flex: 1 1 100%;
  }
  
  .testimonials-grid {
    grid-template-columns: 1fr;
  }
  
  .pricing-plans {
    grid-template-columns: 1fr;
  }
  
  .footer-inner {
    flex-direction: column;
  }
  
  .footer-links {
    flex-direction: column;
    gap: 32px;
  }
  
  .instructor-timeline {
    padding-left: 60px;
  }
  
  .instructor-timeline::before {
    left: 40px;
  }
  
  .timeline-year {
    left: -60px;
    width: 48px;
    font-size: 12px;
  }
  
  .timeline-dot {
    left: -24px;
  }
  
  .chapter-nav {
    flex-direction: column;
    gap: 16px;
  }
  
  .auth-card {
    padding: 32px 24px;
  }
}