/* ============================================
   立体构成学习平台 · 课件视觉体系 v2
   Warm Charcoal + Cyan Teal + Amber Gold
   匹配课件配色 · 层次化灰阶
   ============================================ */

:root {
  /* === 深色基底 — 匹配课件炭灰色体系 === */
  /* 课件主背景: #3A3A3A ~ #4A4A4A */
  --color-bg: #383B40;
  --color-bg-deep: #2C2E32;
  --color-bg-darkest: #232528;

  /* === 层次化表面 — 5级灰阶 === */
  --color-surface: #42454A;
  --color-surface-alt: #3D4045;
  --color-surface-raised: #4A4D52;
  --color-surface-hover: #52555A;
  --color-surface-panel: #5A5E65;

  /* === 文字层次 — 4级 === */
  --color-text-primary: #ECEEF0;
  --color-text-secondary: #B4B8BE;
  --color-text-tertiary: #848890;
  --color-text-faint: #5C5F64;

  /* === 课件标志色 — 青蓝 (Cyan/Teal) === */
  /* 课件: #5CB3CC ~ #7EB8C8 */
  --color-accent: #5CB8CC;
  --color-accent-hover: #72C8DC;
  --color-accent-deep: #4498A8;
  --color-accent-bright: #8ED0E0;
  --color-accent-muted: rgba(92, 184, 204, 0.13);
  --color-accent-glow: rgba(92, 184, 204, 0.08);
  --color-accent-line: rgba(92, 184, 204, 0.25);

  /* === 辅助色 — 暖琥珀 (提取自课件建筑作品) === */
  /* 课件建筑: #C4956A ~ #D4A574 */
  --color-warm: #C4956A;
  --color-warm-hover: #D4A574;
  --color-warm-muted: rgba(196, 149, 106, 0.10);
  --color-warm-glow: rgba(196, 149, 106, 0.06);

  /* === 边框 — 层次化 === */
  --color-border: #50535A;
  --color-border-light: #474A50;
  --color-border-deep: #3E4147;
  --color-border-accent: rgba(92, 184, 204, 0.30);
  --color-border-warm: rgba(196, 149, 106, 0.25);

  /* === 阴影 === */
  --color-shadow-sm: rgba(0, 0, 0, 0.12);
  --color-shadow: rgba(0, 0, 0, 0.22);
  --color-shadow-lg: rgba(0, 0, 0, 0.38);
  --color-glow: rgba(92, 184, 204, 0.15);
  --color-warm-glow-shadow: rgba(196, 149, 106, 0.10);

  /* === 反馈区配色 === */
  --color-good: #7DBB8A;
  --color-good-bg: rgba(125, 187, 138, 0.08);
  --color-good-border: rgba(125, 187, 138, 0.30);
  --color-problem: #D49B6E;
  --color-problem-bg: rgba(212, 155, 110, 0.08);
  --color-problem-border: rgba(212, 155, 110, 0.30);
  --color-suggest: #5CB8CC;
  --color-suggest-bg: rgba(92, 184, 204, 0.08);
  --color-suggest-border: rgba(92, 184, 204, 0.30);
  --color-think: #B89BD4;
  --color-think-bg: rgba(184, 155, 212, 0.08);
  --color-think-border: rgba(184, 155, 212, 0.30);

  /* === 字体 === */
  --font-serif: 'Noto Serif SC', 'Songti SC', serif;
  --font-sans: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-latin: 'Cormorant Garamond', serif;

  /* === 间距 === */
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 40px;
  --space-2xl: 64px;
  --space-3xl: 96px;

  /* === 圆角 === */
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-full: 999px;

  /* === 动画 === */
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-out: cubic-bezier(0, 0, 0.2, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
  --transition: 0.3s var(--ease);
  --transition-slow: 0.5s var(--ease);

  /* === 布局 === */
  --container-max: 1200px;
  --nav-height: 64px;
}

/* ============================================
   Reset
   ============================================ */

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: var(--nav-height);
}

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text-primary);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

/* 背景纹理层 — 模拟课件的层次感与径向渐变 */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  background:
    radial-gradient(ellipse 900px 700px at 12% 8%, rgba(92, 184, 204, 0.04), transparent 60%),
    radial-gradient(ellipse 700px 500px at 88% 85%, rgba(196, 149, 106, 0.03), transparent 60%),
    radial-gradient(ellipse 500px 400px at 50% 50%, rgba(92, 184, 204, 0.015), transparent 70%);
  pointer-events: none;
  z-index: 0;
}

/* 课件几何装饰 — 点阵纹理 */
body::after {
  content: '';
  position: fixed;
  bottom: 0;
  right: 0;
  width: 200px;
  height: 200px;
  background-image: radial-gradient(circle, rgba(92, 184, 204, 0.06) 1px, transparent 1px);
  background-size: 20px 20px;
  pointer-events: none;
  z-index: 0;
  mask-image: linear-gradient(to top left, rgba(0,0,0,0.5), transparent);
  -webkit-mask-image: linear-gradient(to top left, rgba(0,0,0,0.5), transparent);
}

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

button {
  font-family: inherit;
  border: none;
  background: none;
  cursor: pointer;
  color: inherit;
}

textarea {
  font-family: inherit;
  resize: none;
}

a {
  text-decoration: none;
  color: inherit;
}

::selection {
  background: rgba(92, 184, 204, 0.30);
  color: #FFFFFF;
}

/* ============================================
   通用组件
   ============================================ */

.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--space-lg);
  position: relative;
  z-index: 1;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: 12px 28px;
  border-radius: var(--radius-full);
  font-size: 15px;
  font-weight: 500;
  transition: all var(--transition);
  letter-spacing: 0.02em;
  white-space: nowrap;
}

.btn-primary {
  background: var(--color-accent);
  color: #1A1D20;
  font-weight: 600;
  box-shadow: 0 2px 12px var(--color-glow);
}

.btn-primary:hover {
  background: var(--color-accent-hover);
  transform: translateY(-1px);
  box-shadow: 0 6px 28px var(--color-glow);
}

.btn-ghost {
  background: transparent;
  color: var(--color-text-primary);
  border: 1px solid var(--color-border);
}

.btn-ghost:hover {
  background: var(--color-surface-raised);
  border-color: var(--color-border-accent);
  color: var(--color-accent-bright);
}

.btn-sm {
  padding: 8px 20px;
  font-size: 14px;
}

/* ============================================
   导航栏
   ============================================ */

.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(56, 59, 64, 0.6);
  backdrop-filter: blur(24px) saturate(180%);
  -webkit-backdrop-filter: blur(24px) saturate(180%);
  border-bottom: 1px solid transparent;
  z-index: 1000;
  transition: border-color var(--transition), background var(--transition);
}

.nav.scrolled {
  border-bottom-color: var(--color-border-light);
  background: rgba(56, 59, 64, 0.85);
  box-shadow: 0 4px 24px var(--color-shadow-sm);
}

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

.nav-logo {
  display: flex;
  align-items: center;
  gap: 10px;
}

.nav-logo-mark {
  width: 22px;
  height: 22px;
  background: var(--color-accent);
  border-radius: 4px;
  position: relative;
  transform: rotate(45deg);
  transition: transform 0.6s var(--ease);
  box-shadow: 0 2px 8px var(--color-glow);
}

.nav-logo:hover .nav-logo-mark {
  transform: rotate(225deg);
}

.nav-logo-mark::after {
  content: '';
  position: absolute;
  inset: 4px;
  background: var(--color-bg);
  border-radius: 2px;
}

.nav-logo-text {
  font-family: var(--font-serif);
  font-size: 18px;
  font-weight: 600;
  letter-spacing: 0.05em;
  background: linear-gradient(135deg, var(--color-text-primary), var(--color-accent-bright));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.nav-links {
  display: flex;
  gap: var(--space-xl);
}

.nav-link {
  font-size: 14px;
  color: var(--color-text-secondary);
  transition: color var(--transition);
  position: relative;
  padding: 4px 0;
}

.nav-link::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 1.5px;
  background: var(--color-accent);
  transition: width var(--transition);
  border-radius: 1px;
}

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

.nav-link:hover::after,
.nav-link.active::after {
  width: 100%;
}

.nav-link.active {
  color: var(--color-accent);
}

.nav-menu-btn {
  display: none;
  flex-direction: column;
  gap: 4px;
  padding: 8px;
}

.nav-menu-btn span {
  width: 20px;
  height: 1.5px;
  background: var(--color-text-primary);
  transition: all var(--transition);
}

.nav-menu-btn.active span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 5px);
}
.nav-menu-btn.active span:nth-child(2) {
  opacity: 0;
}
.nav-menu-btn.active span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -5px);
}

/* ============================================
   首屏 Hero — 课件封面风格
   ============================================ */

.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  overflow: hidden;
  background: var(--color-bg-deep);
}

/* 课件风格的层叠渐变背景 */
.hero-bg {
  position: absolute;
  inset: 0;
  overflow: hidden;
}

.hero-shape {
  position: absolute;
  border-radius: 50%;
  filter: blur(100px);
}

.hero-shape-1 {
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(92, 184, 204, 0.10), transparent 70%);
  top: -15%;
  right: -8%;
  animation: float1 20s ease-in-out infinite;
}

.hero-shape-2 {
  width: 500px;
  height: 500px;
  background: radial-gradient(circle, rgba(68, 152, 168, 0.08), transparent 70%);
  bottom: -10%;
  left: -8%;
  animation: float2 25s ease-in-out infinite;
}

.hero-shape-3 {
  width: 400px;
  height: 400px;
  background: radial-gradient(circle, rgba(196, 149, 106, 0.06), transparent 70%);
  top: 35%;
  left: 45%;
  animation: float3 30s ease-in-out infinite;
}

/* 课件几何装饰 — 三角形阵列 */
.hero-bg::after {
  content: '';
  position: absolute;
  bottom: 60px;
  right: 80px;
  width: 0;
  height: 0;
  border-left: 12px solid transparent;
  border-right: 12px solid transparent;
  border-bottom: 20px solid rgba(92, 184, 204, 0.10);
  filter: blur(1px);
}

/* 课件点阵装饰 */
.hero-dots {
  position: absolute;
  top: 20%;
  left: 10%;
  width: 120px;
  height: 120px;
  background-image: radial-gradient(circle, rgba(92, 184, 204, 0.12) 1.5px, transparent 1.5px);
  background-size: 24px 24px;
  opacity: 0.6;
  mask-image: radial-gradient(circle, rgba(0,0,0,1), transparent 70%);
  -webkit-mask-image: radial-gradient(circle, rgba(0,0,0,1), transparent 70%);
}

@keyframes float1 {
  0%, 100% { transform: translate(0, 0) scale(1); }
  50% { transform: translate(-30px, 40px) scale(1.05); }
}

@keyframes float2 {
  0%, 100% { transform: translate(0, 0) scale(1); }
  50% { transform: translate(40px, -30px) scale(0.95); }
}

@keyframes float3 {
  0%, 100% { transform: translateX(-50%) scale(1); }
  50% { transform: translateX(-50%) translateY(30px) scale(1.1); }
}

.hero-content {
  position: relative;
  z-index: 1;
  text-align: center;
  max-width: 700px;
  padding: 0 var(--space-lg);
  animation: heroFadeIn 1.2s var(--ease-out) both;
}

@keyframes heroFadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

.hero-tag {
  font-family: var(--font-latin);
  font-size: 15px;
  letter-spacing: 0.15em;
  color: var(--color-accent);
  text-transform: uppercase;
  margin-bottom: var(--space-lg);
}

.hero-title {
  font-family: var(--font-serif);
  font-size: clamp(48px, 8vw, 96px);
  font-weight: 300;
  letter-spacing: 0.1em;
  color: var(--color-text-primary);
  margin-bottom: var(--space-lg);
  line-height: 1.1;
  /* 课件标题青色光效 */
  text-shadow: 0 0 60px rgba(92, 184, 204, 0.20);
}

.hero-subtitle {
  font-size: 17px;
  color: var(--color-text-secondary);
  line-height: 1.8;
  margin-bottom: var(--space-xl);
  font-weight: 300;
}

.hero-meta {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-md);
  margin-bottom: var(--space-2xl);
  flex-wrap: wrap;
}

.hero-meta-item {
  font-size: 13px;
  color: var(--color-text-tertiary);
  letter-spacing: 0.03em;
}

.hero-meta-divider {
  width: 4px;
  height: 4px;
  background: var(--color-text-faint);
  border-radius: 50%;
}

.hero-actions {
  display: flex;
  gap: var(--space-md);
  justify-content: center;
}

.hero-scroll {
  position: absolute;
  bottom: 32px;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-sm);
  z-index: 1;
}

.hero-scroll span {
  font-size: 12px;
  color: var(--color-text-tertiary);
  letter-spacing: 0.1em;
}

.hero-scroll-line {
  width: 1px;
  height: 40px;
  background: linear-gradient(to bottom, var(--color-accent), transparent);
  animation: scrollLine 2s var(--ease) infinite;
}

@keyframes scrollLine {
  0% { transform: scaleY(0); transform-origin: top; }
  50% { transform: scaleY(1); transform-origin: top; }
  51% { transform-origin: bottom; }
  100% { transform: scaleY(0); transform-origin: bottom; }
}

/* ============================================
   Section 通用
   ============================================ */

.section {
  padding: var(--space-3xl) 0;
  position: relative;
}

.section-alt {
  background: var(--color-surface-alt);
}

/* Section间渐变过渡 */
.section-alt::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 100px;
  background: linear-gradient(to bottom, var(--color-bg), transparent);
  pointer-events: none;
}

.section-alt::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 100px;
  background: linear-gradient(to top, var(--color-bg), transparent);
  pointer-events: none;
}

.section-header {
  text-align: center;
  margin-bottom: var(--space-2xl);
}

.section-label {
  font-family: var(--font-latin);
  font-size: 14px;
  letter-spacing: 0.15em;
  color: var(--color-accent);
  text-transform: uppercase;
  margin-bottom: var(--space-md);
}

.section-title {
  font-family: var(--font-serif);
  font-size: clamp(32px, 5vw, 48px);
  font-weight: 400;
  color: var(--color-text-primary);
  margin-bottom: var(--space-md);
  letter-spacing: 0.03em;
}

.section-desc {
  font-size: 15px;
  color: var(--color-text-secondary);
  max-width: 500px;
  margin: 0 auto;
  line-height: 1.8;
}

/* ============================================
   课程概览 - 章节卡片
   ============================================ */

.chapters {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(500px, 1fr));
  gap: var(--space-xl);
  margin-bottom: var(--space-2xl);
}

.chapter-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  border: 1px solid var(--color-border-light);
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

/* 卡片顶部双色光效 — 青蓝+暖琥珀 */
.chapter-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent 10%, var(--color-accent-line) 40%, var(--color-border-warm) 60%, transparent 90%);
  opacity: 0;
  transition: opacity var(--transition);
}

/* 卡片右上角课件几何装饰 */
.chapter-card::after {
  content: '';
  position: absolute;
  top: 20px;
  right: 20px;
  width: 0;
  height: 0;
  border-left: 8px solid transparent;
  border-right: 8px solid transparent;
  border-bottom: 14px solid var(--color-border-light);
  opacity: 0.6;
  transition: all var(--transition);
}

.chapter-card:hover {
  border-color: var(--color-border);
  box-shadow: 0 16px 48px var(--color-shadow);
  transform: translateY(-2px);
}

.chapter-card:hover::before {
  opacity: 1;
}

.chapter-card:hover::after {
  border-bottom-color: var(--color-accent);
  transform: translateY(4px);
  opacity: 1;
}

.chapter-card-header {
  display: flex;
  align-items: baseline;
  gap: var(--space-md);
  margin-bottom: var(--space-lg);
}

.chapter-card-number {
  font-family: var(--font-latin);
  font-size: 48px;
  font-weight: 300;
  color: var(--color-text-faint);
  line-height: 1;
  transition: color var(--transition);
}

.chapter-card:hover .chapter-card-number {
  color: var(--color-accent-deep);
}

.chapter-card-title {
  font-family: var(--font-serif);
  font-size: 22px;
  font-weight: 500;
  color: var(--color-text-primary);
}

.chapter-card-subtitle {
  font-size: 14px;
  color: var(--color-text-tertiary);
  margin-bottom: var(--space-lg);
}

.chapter-card-keywords {
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
  margin-bottom: var(--space-lg);
}

.chapter-keyword {
  padding: 4px 12px;
  background: var(--color-accent-muted);
  color: var(--color-accent-bright);
  border-radius: var(--radius-full);
  font-size: 12px;
  letter-spacing: 0.03em;
  border: 1px solid var(--color-border-deep);
}

.chapter-card-sections {
  border-top: 1px solid var(--color-border-light);
  padding-top: var(--space-lg);
}

.chapter-section-item {
  padding: var(--space-md) 0;
  border-bottom: 1px solid var(--color-border-deep);
}

.chapter-section-item:last-child {
  border-bottom: none;
}

.chapter-section-title {
  font-size: 14px;
  font-weight: 500;
  color: var(--color-text-primary);
  margin-bottom: var(--space-xs);
}

.chapter-section-content {
  font-size: 13px;
  color: var(--color-text-secondary);
  line-height: 1.8;
}

/* ============================================
   核心概念
   ============================================ */

.concepts {
  margin-top: var(--space-2xl);
}

.concepts-title {
  font-family: var(--font-serif);
  font-size: 24px;
  font-weight: 400;
  color: var(--color-text-primary);
  margin-bottom: var(--space-xl);
  text-align: center;
}

.concepts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: var(--space-md);
}

.concept-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  transition: all var(--transition);
  cursor: default;
  position: relative;
  overflow: hidden;
}

/* 概念卡片左上角点阵装饰 */
.concept-card::before {
  content: '';
  position: absolute;
  top: 12px;
  right: 12px;
  width: 6px;
  height: 6px;
  background: var(--color-accent);
  border-radius: 50%;
  opacity: 0.3;
  transition: opacity var(--transition);
}

.concept-card:hover {
  border-color: var(--color-border-accent);
  box-shadow: 0 8px 32px var(--color-shadow), 0 0 0 1px var(--color-border-accent);
  background: var(--color-surface-raised);
}

.concept-card:hover::before {
  opacity: 1;
  box-shadow: 0 0 8px var(--color-glow);
}

.concept-term {
  font-family: var(--font-serif);
  font-size: 17px;
  font-weight: 500;
  color: var(--color-text-primary);
  margin-bottom: var(--space-sm);
  padding-left: var(--space-sm);
  border-left: 2px solid var(--color-accent);
}

.concept-def {
  font-size: 13px;
  color: var(--color-text-secondary);
  line-height: 1.7;
}

/* ============================================
   自主问答
   ============================================ */

.qa-layout {
  max-width: 800px;
  margin: 0 auto;
}

.qa-main {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-light);
  overflow: hidden;
  display: flex;
  flex-direction: column;
  box-shadow: 0 8px 40px var(--color-shadow-sm);
}

.qa-chat {
  padding: var(--space-xl);
  min-height: 360px;
  max-height: 500px;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
}

.qa-chat::-webkit-scrollbar {
  width: 4px;
}

.qa-chat::-webkit-scrollbar-track {
  background: transparent;
}

.qa-chat::-webkit-scrollbar-thumb {
  background: var(--color-border);
  border-radius: 2px;
}

.qa-message {
  display: flex;
  gap: var(--space-md);
  animation: messageSlide 0.4s var(--ease-out) both;
}

@keyframes messageSlide {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.qa-message-user {
  flex-direction: row-reverse;
}

.qa-avatar {
  flex-shrink: 0;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: var(--color-accent);
  color: #1A1D20;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.05em;
  box-shadow: 0 2px 8px var(--color-glow);
}

.qa-message-user .qa-avatar {
  background: var(--color-surface-panel);
  color: var(--color-text-secondary);
  box-shadow: none;
}

.qa-bubble {
  background: var(--color-surface-alt);
  border-radius: var(--radius-md);
  padding: var(--space-md) var(--space-lg);
  max-width: 80%;
  font-size: 14px;
  line-height: 1.8;
  color: var(--color-text-primary);
  border: 1px solid var(--color-border-deep);
}

.qa-message-user .qa-bubble {
  background: var(--color-accent-deep);
  color: #FFFFFF;
  border-color: var(--color-accent-deep);
}

.qa-bubble p {
  margin-bottom: var(--space-sm);
}

.qa-bubble p:last-child {
  margin-bottom: 0;
}

.qa-bubble strong {
  font-weight: 600;
  color: var(--color-accent-bright);
}

.qa-message-user .qa-bubble strong {
  color: #FFFFFF;
}

.qa-bubble code {
  background: var(--color-accent-muted);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 13px;
  color: var(--color-accent-bright);
}

.qa-bubble blockquote {
  border-left: 2px solid var(--color-accent);
  padding-left: var(--space-md);
  margin: var(--space-sm) 0;
  color: var(--color-text-secondary);
  font-style: italic;
}

.qa-bubble ul, .qa-bubble ol {
  padding-left: var(--space-lg);
  margin-bottom: var(--space-sm);
}

.qa-bubble li {
  margin-bottom: 4px;
}

.qa-bubble h3 {
  font-family: var(--font-serif);
  font-size: 16px;
  margin: var(--space-md) 0 var(--space-sm);
  color: var(--color-accent-bright);
}

/* 问答来源标签 */
.qa-sources {
  margin-top: var(--space-md);
  padding-top: var(--space-md);
  border-top: 1px solid var(--color-border-deep);
}

.qa-source-label {
  font-size: 11px;
  color: var(--color-text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: var(--space-sm);
}

.qa-source-tags {
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
}

.qa-source-tag {
  font-size: 11px;
  padding: 3px 10px;
  border-radius: var(--radius-full);
  background: var(--color-surface-hover);
  color: var(--color-text-secondary);
}

.qa-source-tag.web {
  background: var(--color-accent-muted);
  color: var(--color-accent-bright);
  border: 1px solid var(--color-border-deep);
}

.qa-suggestions {
  padding: var(--space-md) var(--space-xl);
  border-top: 1px solid var(--color-border-deep);
  border-bottom: 1px solid var(--color-border-deep);
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
  background: var(--color-bg-deep);
}

.qa-suggestion-chip {
  padding: 6px 14px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-full);
  font-size: 13px;
  color: var(--color-text-secondary);
  transition: all var(--transition);
}

.qa-suggestion-chip:hover {
  border-color: var(--color-border-accent);
  color: var(--color-accent-bright);
  background: var(--color-accent-muted);
}

.qa-input-area {
  padding: var(--space-md) var(--space-xl) var(--space-lg);
}

.qa-input-wrap {
  display: flex;
  gap: var(--space-sm);
  align-items: flex-end;
  background: var(--color-bg-deep);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-sm) var(--space-md);
  transition: all var(--transition);
}

.qa-input-wrap:focus-within {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px var(--color-accent-muted);
}

.qa-input {
  flex: 1;
  border: none;
  background: transparent;
  font-size: 14px;
  color: var(--color-text-primary);
  line-height: 1.6;
  padding: 8px 0;
  outline: none;
}

.qa-input::placeholder {
  color: var(--color-text-faint);
}

.qa-send {
  flex-shrink: 0;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: var(--color-accent);
  color: #1A1D20;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
}

.qa-send:hover {
  background: var(--color-accent-hover);
  transform: scale(1.05);
  box-shadow: 0 4px 20px var(--color-glow);
}

.qa-send:disabled {
  background: var(--color-text-faint);
  cursor: not-allowed;
  transform: none;
}

.qa-status {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  margin-top: var(--space-md);
  font-size: 12px;
  color: var(--color-text-tertiary);
}

.qa-status-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--color-accent);
  animation: pulse 2s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; box-shadow: 0 0 8px var(--color-glow); }
  50% { opacity: 0.4; }
}

/* 打字动画 */
.typing-indicator {
  display: flex;
  gap: 4px;
  align-items: center;
  padding: var(--space-sm) 0;
}

.typing-indicator span {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--color-accent);
  animation: typing 1.4s ease-in-out infinite;
}

.typing-indicator span:nth-child(2) { animation-delay: 0.2s; }
.typing-indicator span:nth-child(3) { animation-delay: 0.4s; }

@keyframes typing {
  0%, 60%, 100% { transform: translateY(0); opacity: 0.4; }
  30% { transform: translateY(-6px); opacity: 1; }
}

/* ============================================
   AI 助手
   ============================================ */

.assistant-layout {
  display: grid;
  grid-template-columns: 1fr 1.2fr;
  gap: var(--space-xl);
}

.assistant-left {
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
}

.assistant-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-light);
  padding: var(--space-xl);
  position: relative;
  overflow: hidden;
}

/* 助手卡片顶部双色条 */
.assistant-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: var(--space-xl);
  right: var(--space-xl);
  height: 2px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-warm));
  border-radius: 0 0 2px 2px;
  opacity: 0.4;
  transition: opacity var(--transition);
}

.assistant-card:hover::before {
  opacity: 0.8;
}

.assistant-card-label {
  font-size: 12px;
  color: var(--color-accent);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: var(--space-md);
  font-weight: 500;
}

.question-selector {
  display: flex;
  flex-direction: column;
  gap: var(--space-sm);
  max-height: 280px;
  overflow-y: auto;
}

.question-selector::-webkit-scrollbar {
  width: 4px;
}

.question-selector::-webkit-scrollbar-thumb {
  background: var(--color-border);
  border-radius: 2px;
}

.question-item {
  padding: var(--space-md);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition);
  display: flex;
  gap: var(--space-md);
  align-items: flex-start;
}

.question-item:hover {
  border-color: var(--color-border-accent);
  background: var(--color-surface-hover);
}

.question-item.active {
  border-color: var(--color-accent);
  background: var(--color-accent-muted);
}

.question-item-number {
  flex-shrink: 0;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  border: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 11px;
  color: var(--color-text-tertiary);
  transition: all var(--transition);
}

.question-item.active .question-item-number {
  background: var(--color-accent);
  color: #1A1D20;
  border-color: var(--color-accent);
}

.question-item-content {
  flex: 1;
}

.question-item-text {
  font-size: 14px;
  color: var(--color-text-primary);
  line-height: 1.6;
  margin-bottom: 4px;
}

.question-item-hint {
  font-size: 12px;
  color: var(--color-text-tertiary);
}

.question-item-category {
  font-size: 11px;
  color: var(--color-accent);
  margin-top: 4px;
}

.answer-input-wrap {
  margin-top: var(--space-sm);
}

.answer-input {
  width: 100%;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-md);
  font-size: 14px;
  line-height: 1.7;
  color: var(--color-text-primary);
  background: var(--color-bg-deep);
  transition: all var(--transition);
  outline: none;
}

.answer-input:focus {
  border-color: var(--color-accent);
  background: var(--color-surface);
  box-shadow: 0 0 0 3px var(--color-accent-muted);
}

.answer-input::placeholder {
  color: var(--color-text-faint);
}

.answer-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: var(--space-md);
}

.answer-meta span {
  font-size: 12px;
  color: var(--color-text-tertiary);
}

/* 反馈区 */
.assistant-right {
  position: sticky;
  top: calc(var(--nav-height) + var(--space-lg));
  align-self: flex-start;
}

.feedback-area {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-light);
  min-height: 500px;
  overflow: hidden;
}

.feedback-placeholder {
  height: 500px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: var(--space-2xl);
  color: var(--color-text-tertiary);
}

.feedback-placeholder-icon {
  margin-bottom: var(--space-lg);
  color: var(--color-text-faint);
  animation: gentleFloat 4s ease-in-out infinite;
}

@keyframes gentleFloat {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-8px); }
}

.feedback-placeholder-title {
  font-family: var(--font-serif);
  font-size: 20px;
  font-weight: 400;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-sm);
}

.feedback-placeholder-desc {
  font-size: 14px;
  color: var(--color-text-tertiary);
  line-height: 1.8;
}

/* 反馈内容 */
.feedback-content {
  padding: var(--space-xl);
  animation: feedbackFadeIn 0.6s var(--ease-out) both;
}

@keyframes feedbackFadeIn {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

.feedback-header {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-lg);
  border-bottom: 1px solid var(--color-border);
}

.feedback-header-icon {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--color-accent-muted);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-accent);
  box-shadow: 0 2px 12px var(--color-glow);
}

.feedback-header-text {
  flex: 1;
}

.feedback-header-title {
  font-family: var(--font-serif);
  font-size: 18px;
  font-weight: 500;
  color: var(--color-text-primary);
}

.feedback-header-sub {
  font-size: 12px;
  color: var(--color-text-tertiary);
  margin-top: 2px;
}

.feedback-section {
  margin-bottom: var(--space-lg);
  padding: var(--space-lg);
  border-radius: var(--radius-md);
  border-left: 3px solid;
  animation: feedbackSectionIn 0.5s var(--ease-out) both;
}

.feedback-section:nth-child(2) { animation-delay: 0.1s; }
.feedback-section:nth-child(3) { animation-delay: 0.2s; }
.feedback-section:nth-child(4) { animation-delay: 0.3s; }
.feedback-section:nth-child(5) { animation-delay: 0.4s; }

@keyframes feedbackSectionIn {
  from { opacity: 0; transform: translateX(-8px); }
  to { opacity: 1; transform: translateX(0); }
}

.feedback-section.good {
  background: var(--color-good-bg);
  border-left-color: var(--color-good);
}

.feedback-section.problem {
  background: var(--color-problem-bg);
  border-left-color: var(--color-problem);
}

.feedback-section.suggest {
  background: var(--color-suggest-bg);
  border-left-color: var(--color-suggest);
}

.feedback-section.think {
  background: var(--color-think-bg);
  border-left-color: var(--color-think);
}

.feedback-section-label {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: 13px;
  font-weight: 600;
  margin-bottom: var(--space-sm);
  letter-spacing: 0.03em;
}

.feedback-section.good .feedback-section-label { color: var(--color-good); }
.feedback-section.problem .feedback-section-label { color: var(--color-problem); }
.feedback-section.suggest .feedback-section-label { color: var(--color-suggest); }
.feedback-section.think .feedback-section-label { color: var(--color-think); }

.feedback-section-number {
  width: 22px;
  height: 22px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 11px;
  font-family: var(--font-latin);
}

.feedback-section.good .feedback-section-number { background: var(--color-good); color: #1A1D20; }
.feedback-section.problem .feedback-section-number { background: var(--color-problem); color: #1A1D20; }
.feedback-section.suggest .feedback-section-number { background: var(--color-suggest); color: #1A1D20; }
.feedback-section.think .feedback-section-number { background: var(--color-think); color: #1A1D20; }

.feedback-section-content {
  font-size: 14px;
  line-height: 1.8;
  color: var(--color-text-primary);
}

.feedback-section-content p {
  margin-bottom: var(--space-sm);
}

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

.feedback-section-content strong {
  font-weight: 600;
}

.feedback-loading {
  padding: var(--space-2xl);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-lg);
  min-height: 400px;
}

.feedback-loading-text {
  font-size: 14px;
  color: var(--color-accent);
  font-family: var(--font-serif);
}

/* ============================================
   课件浏览
   ============================================ */

.slides-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: var(--space-md);
}

.slide-thumb {
  position: relative;
  aspect-ratio: 16 / 9;
  border-radius: var(--radius-md);
  overflow: hidden;
  cursor: pointer;
  border: 1px solid var(--color-border-light);
  transition: all var(--transition);
  background: var(--color-surface);
}

.slide-thumb:hover {
  border-color: var(--color-accent);
  box-shadow: 0 12px 40px var(--color-shadow), 0 0 0 1px var(--color-border-accent);
  transform: translateY(-3px);
}

.slide-thumb img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.6s var(--ease);
}

.slide-thumb:hover img {
  transform: scale(1.05);
}

.slide-thumb-overlay {
  position: absolute;
  inset: 0;
  background: linear-gradient(to top, rgba(35, 37, 40, 0.85), transparent 50%);
  display: flex;
  align-items: flex-end;
  padding: var(--space-sm) var(--space-md);
  opacity: 0;
  transition: opacity var(--transition);
}

.slide-thumb:hover .slide-thumb-overlay {
  opacity: 1;
}

.slide-thumb-number {
  font-family: var(--font-latin);
  font-size: 14px;
  color: var(--color-accent-bright);
  font-weight: 500;
}

/* 幻灯片弹窗 */
.slide-modal {
  position: fixed;
  inset: 0;
  z-index: 2000;
  display: none;
  align-items: center;
  justify-content: center;
}

.slide-modal.active {
  display: flex;
}

.slide-modal-bg {
  position: absolute;
  inset: 0;
  background: rgba(28, 30, 33, 0.95);
  backdrop-filter: blur(16px);
}

.slide-modal-content {
  position: relative;
  z-index: 1;
  max-width: 90vw;
  max-height: 85vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

.slide-modal-img {
  max-width: 100%;
  max-height: 85vh;
  border-radius: var(--radius-md);
  box-shadow: 0 32px 96px rgba(0,0,0,0.7), 0 0 0 1px var(--color-border);
}

.slide-modal-close {
  position: absolute;
  top: -40px;
  right: 0;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: rgba(255,255,255,0.08);
  color: #FFFFFF;
  font-size: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
}

.slide-modal-close:hover {
  background: rgba(92, 184, 204, 0.25);
  transform: rotate(90deg);
}

.slide-modal-nav {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: rgba(255,255,255,0.08);
  color: #FFFFFF;
  font-size: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
}

.slide-modal-nav:hover {
  background: rgba(92, 184, 204, 0.25);
}

.slide-modal-prev { left: -64px; }
.slide-modal-next { right: -64px; }

.slide-modal-info {
  position: absolute;
  bottom: -32px;
  left: 50%;
  transform: translateX(-50%);
  font-size: 13px;
  color: rgba(255,255,255,0.5);
  font-family: var(--font-latin);
}

/* ============================================
   页脚
   ============================================ */

.footer {
  background: var(--color-bg-deep);
  border-top: 1px solid var(--color-border-light);
  padding: var(--space-2xl) 0;
  position: relative;
  overflow: hidden;
}

/* 页脚顶部双色光条 */
.footer::before {
  content: '';
  position: absolute;
  top: 0;
  left: 20%;
  right: 20%;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--color-accent-line) 30%, var(--color-border-warm) 70%, transparent);
}

.footer-inner {
  text-align: center;
}

.footer-brand {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  margin-bottom: var(--space-md);
}

.footer-brand-mark {
  width: 20px;
  height: 20px;
  background: var(--color-accent);
  border-radius: 3px;
  transform: rotate(45deg);
  position: relative;
  box-shadow: 0 2px 8px var(--color-glow);
}

.footer-brand-mark::after {
  content: '';
  position: absolute;
  inset: 3px;
  background: var(--color-bg-deep);
  border-radius: 1.5px;
}

.footer-brand span:last-child {
  font-family: var(--font-serif);
  font-size: 16px;
  font-weight: 500;
  letter-spacing: 0.03em;
  color: var(--color-text-primary);
}

.footer-text {
  font-size: 13px;
  color: var(--color-text-tertiary);
  margin-bottom: var(--space-sm);
}

.footer-copy {
  font-size: 12px;
  color: var(--color-text-faint);
  font-family: var(--font-latin);
  letter-spacing: 0.05em;
}

/* ============================================
   加载动画
   ============================================ */

.loader {
  position: fixed;
  inset: 0;
  background: var(--color-bg-deep);
  z-index: 9999;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: opacity 0.6s var(--ease), visibility 0.6s var(--ease);
}

.loader.hidden {
  opacity: 0;
  visibility: hidden;
}

.loader-spinner {
  width: 40px;
  height: 40px;
  border: 2px solid var(--color-border);
  border-top-color: var(--color-accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* ============================================
   响应式
   ============================================ */

@media (max-width: 900px) {
  .assistant-layout {
    grid-template-columns: 1fr;
  }

  .assistant-right {
    position: static;
  }

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

@media (max-width: 768px) {
  .nav-links {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: var(--color-surface);
    flex-direction: column;
    padding: var(--space-lg);
    gap: var(--space-md);
    border-bottom: 1px solid var(--color-border);
  }

  .nav-links.open {
    display: flex;
  }

  .nav-menu-btn {
    display: flex;
  }

  .section {
    padding: var(--space-2xl) 0;
  }

  .hero-actions {
    flex-direction: column;
    align-items: stretch;
  }

  .qa-suggestions {
    flex-direction: column;
  }

  .slide-modal-prev { left: 8px; }
  .slide-modal-next { right: 8px; }

  .slides-grid {
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  }
}

@media (max-width: 480px) {
  .hero-meta {
    flex-direction: column;
    gap: var(--space-sm);
  }

  .hero-meta-divider {
    display: none;
  }

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