/* ==========================================================================
   ARK 网络加速服务 - 核心视觉样式表 (黑白极简风格)
   Design: Modern Monochrome Minimalist (Black, White, Neutral Grays)
   Typography: Native Rounded Sans-Serif, High Readability
   ========================================================================== */

:root {
  /* 黑白极简调色板 */
  --bg-primary: #0a0a0c;
  --bg-secondary: #121216;
  --bg-tertiary: #18181e;
  --bg-elevated: #22222b;
  --bg-card: rgba(20, 20, 25, 0.7);
  --bg-card-hover: rgba(28, 28, 36, 0.9);

  --border-subtle: #23232a;
  --border-medium: #34343f;
  --border-strong: #4f4f5e;
  --border-light: rgba(255, 255, 255, 0.15);

  --text-primary: #ffffff;
  --text-secondary: #d1d5db;
  --text-muted: #9ca3af;
  --text-disabled: #4b5563;
  --text-inverse: #0a0a0c;

  --accent-white: #ffffff;
  --accent-light: #f3f4f6;
  --accent-gray: #71717a;
  --status-live: #22c55e;
  --status-info: #e5e7eb;

  /* 阴影与微光 */
  --shadow-subtle: 0 4px 20px rgba(0, 0, 0, 0.4);
  --shadow-elevated: 0 10px 40px rgba(0, 0, 0, 0.6);
  --glow-light: 0 0 24px rgba(255, 255, 255, 0.08);

  /* 间距与尺寸 */
  --container-max: 1200px;
  --container-narrow: 880px;
  --nav-height: 74px;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-pill: 9999px;

  /* 字体系统 - 粗圆现代几何风 */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-heading: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;

  /* 过渡曲线 */
  --transition-fast: 0.18s cubic-bezier(0.16, 1, 0.3, 1);
  --transition-normal: 0.28s cubic-bezier(0.16, 1, 0.3, 1);
  --transition-slow: 0.45s cubic-bezier(0.16, 1, 0.3, 1);
}

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

html {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  scroll-behavior: smooth;
  text-rendering: optimizeLegibility;
}

body {
  min-height: 100vh;
  background-color: var(--bg-primary);
  color: var(--text-secondary);
  overflow-x: hidden;
  position: relative;
  font-size: 16px;
}

/* 焦点环无障碍反馈 */
a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible {
  outline: 2px solid var(--accent-white);
  outline-offset: 3px;
  border-radius: 4px;
}

/* 背景细腻噪点网格纹理（纯CSS轻量装饰） */
.bg-grid-pattern {
  position: fixed;
  inset: 0;
  background-image: 
    linear-gradient(to right, rgba(255, 255, 255, 0.02) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(255, 255, 255, 0.02) 1px, transparent 1px);
  background-size: 48px 48px;
  pointer-events: none;
  z-index: 0;
}

/* 容器定义 */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-left: auto;
  margin-right: auto;
  padding-left: 24px;
  padding-right: 24px;
  position: relative;
  z-index: 1;
}

.container-narrow {
  max-width: var(--container-narrow);
}

/* 排版体系 */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  color: var(--text-primary);
  font-weight: 700;
  line-height: 1.25;
  letter-spacing: -0.02em;
}

.brand-ark-title {
  font-family: var(--font-heading);
  font-weight: 900;
  letter-spacing: -0.035em;
  color: var(--accent-white);
  text-transform: uppercase;
}

/* 按钮规范 */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  font-weight: 600;
  font-size: 15px;
  padding: 12px 26px;
  border-radius: var(--radius-pill);
  cursor: pointer;
  text-decoration: none;
  transition: all var(--transition-fast);
  border: 1px solid transparent;
  user-select: none;
  white-space: nowrap;
}

.btn-primary {
  background-color: var(--accent-white);
  color: var(--text-inverse);
  box-shadow: 0 4px 14px rgba(255, 255, 255, 0.15);
}

.btn-primary:hover {
  background-color: var(--accent-light);
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(255, 255, 255, 0.25);
}

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

.btn-secondary:hover {
  background-color: var(--bg-tertiary);
  border-color: var(--border-strong);
  color: var(--accent-white);
  transform: translateY(-2px);
}

.btn-sm {
  padding: 8px 18px;
  font-size: 13px;
}

.btn-lg {
  padding: 15px 34px;
  font-size: 17px;
  font-weight: 700;
}

.btn:active {
  transform: translateY(0);
}

/* 胶囊徽章 Badge */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 14px;
  border-radius: var(--radius-pill);
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-medium);
  color: var(--text-secondary);
}

.badge-live::before {
  content: "";
  display: inline-block;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background-color: var(--status-live);
  box-shadow: 0 0 10px var(--status-live);
}

/* ==========================================================================
   页眉 Header & Navigation
   ========================================================================== */
.site-header {
  position: sticky;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background-color: rgba(10, 10, 12, 0.85);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-subtle);
  z-index: 100;
  transition: border-color var(--transition-fast);
}

.header-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.brand-logo-link {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text-primary);
  font-weight: 900;
  font-size: 22px;
  letter-spacing: -0.04em;
  transition: opacity var(--transition-fast);
}

.brand-logo-link:hover {
  opacity: 0.85;
}

.brand-logo-icon {
  width: 34px;
  height: 34px;
  border-radius: 9px;
  background: #ffffff;
  color: #000000;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 900;
  font-size: 18px;
}

.nav-desktop {
  display: flex;
  align-items: center;
  gap: 28px;
}

.nav-link {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  transition: color var(--transition-fast);
  position: relative;
  padding: 6px 2px;
}

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

.nav-link.special-link {
  color: var(--text-primary);
  font-weight: 600;
}

.nav-link.special-link::after {
  content: "NEW";
  font-size: 9px;
  padding: 1px 5px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-strong);
  border-radius: 4px;
  margin-left: 5px;
  vertical-align: middle;
  color: var(--accent-light);
}

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

.mobile-menu-toggle {
  display: none;
  background: none;
  border: 1px solid var(--border-medium);
  color: var(--text-primary);
  padding: 8px;
  border-radius: var(--radius-sm);
  cursor: pointer;
}

/* ==========================================================================
   移动端抽屉导航
   ========================================================================== */
.mobile-nav-drawer {
  display: none;
  position: fixed;
  top: var(--nav-height);
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(10, 10, 12, 0.98);
  backdrop-filter: blur(20px);
  z-index: 99;
  padding: 32px 24px;
  flex-direction: column;
  gap: 20px;
  border-top: 1px solid var(--border-subtle);
  overflow-y: auto;
}

.mobile-nav-drawer.open {
  display: flex;
}

.mobile-nav-link {
  font-size: 18px;
  font-weight: 600;
  color: var(--text-primary);
  text-decoration: none;
  padding: 12px 0;
  border-bottom: 1px solid var(--border-subtle);
}

/* ==========================================================================
   章节统一定义
   ========================================================================== */
.page-section {
  padding: 96px 0;
  position: relative;
  border-bottom: 1px solid rgba(255, 255, 255, 0.04);
}

.section-header {
  text-align: center;
  margin-bottom: 56px;
  max-width: 680px;
  margin-left: auto;
  margin-right: auto;
}

.section-tag {
  margin-bottom: 14px;
}

.section-title {
  font-size: 36px;
  font-weight: 800;
  margin-bottom: 16px;
  color: var(--accent-white);
  letter-spacing: -0.025em;
}

.section-subtitle {
  font-size: 16px;
  color: var(--text-muted);
  line-height: 1.6;
}

/* ==========================================================================
   主视觉 Hero Section
   ========================================================================== */
.hero-section {
  padding: 90px 0 110px 0;
  min-height: calc(88vh - var(--nav-height));
  display: flex;
  align-items: center;
}

.hero-layout {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 56px;
  align-items: center;
}

.hero-text-content {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.hero-main-title {
  font-size: clamp(38px, 5.2vw, 56px);
  font-weight: 900;
  line-height: 1.12;
  letter-spacing: -0.035em;
  color: var(--accent-white);
}

.hero-brand-name {
  display: inline-block;
  padding: 0 8px;
  background: #ffffff;
  color: #000000;
  border-radius: 8px;
  margin-right: 8px;
}

.hero-description {
  font-size: 18px;
  color: var(--text-muted);
  line-height: 1.7;
  max-width: 580px;
}

.hero-cta-group {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
  margin-top: 8px;
}

.hero-metrics {
  display: flex;
  align-items: center;
  gap: 36px;
  padding-top: 24px;
  border-top: 1px solid var(--border-subtle);
  margin-top: 12px;
}

.metric-item {
  display: flex;
  flex-direction: column;
}

.metric-number {
  font-size: 24px;
  font-weight: 800;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.metric-label {
  font-size: 13px;
  color: var(--text-muted);
}

/* Hero 右侧动态卡片 (桌面端高科技黑白极简控制面板) */
.hero-interactive-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-lg);
  padding: 28px;
  box-shadow: var(--shadow-elevated);
  position: relative;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  gap: 22px;
}

.hero-card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--border-subtle);
  padding-bottom: 16px;
}

.hero-card-status {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 13px;
  color: var(--text-secondary);
  font-weight: 600;
}

.node-ping-display {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-subtle);
  padding: 14px 18px;
  border-radius: var(--radius-md);
}

.node-icon {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--status-live);
  box-shadow: 0 0 10px var(--status-live);
}

.node-info-text {
  flex: 1;
}

.node-name {
  font-size: 14px;
  font-weight: 700;
  color: var(--text-primary);
}

.node-route {
  font-size: 12px;
  color: var(--text-muted);
}

.node-latency {
  font-family: monospace;
  font-weight: 700;
  font-size: 14px;
  color: var(--accent-white);
  background: var(--bg-elevated);
  padding: 4px 8px;
  border-radius: 6px;
}

/* 动效波形与模拟吞吐量 */
.bandwidth-meter-card {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-subtle);
  padding: 18px;
  border-radius: var(--radius-md);
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.meter-title-row {
  display: flex;
  justify-content: space-between;
  font-size: 12px;
  color: var(--text-muted);
}

.meter-bar-track {
  height: 6px;
  background: var(--border-subtle);
  border-radius: 3px;
  overflow: hidden;
  position: relative;
}

.meter-bar-fill {
  height: 100%;
  width: 94%;
  background: #ffffff;
  border-radius: 3px;
}

.protocol-tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.protocol-chip {
  font-size: 11px;
  font-weight: 600;
  padding: 4px 10px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-medium);
  border-radius: 6px;
  color: var(--text-secondary);
}

/* ==========================================================================
   核心优势 Features Grid (3-6 卡片)
   ========================================================================== */
.features-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}

.feature-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 32px 26px;
  transition: all var(--transition-normal);
  display: flex;
  flex-direction: column;
  gap: 16px;
  position: relative;
}

.feature-card:hover {
  background: var(--bg-tertiary);
  border-color: var(--border-strong);
  transform: translateY(-4px);
  box-shadow: var(--shadow-elevated);
}

.feature-icon-wrapper {
  width: 48px;
  height: 48px;
  border-radius: 12px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-medium);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--accent-white);
}

.feature-title {
  font-size: 19px;
  font-weight: 700;
  color: var(--text-primary);
}

.feature-text {
  font-size: 14px;
  color: var(--text-muted);
  line-height: 1.65;
}

/* ==========================================================================
   流媒体与 AI 支持 Section
   ========================================================================== */
.streaming-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
  margin-bottom: 32px;
}

.service-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 24px 20px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  text-align: center;
  align-items: center;
  transition: border-color var(--transition-fast);
}

.service-card:hover {
  border-color: var(--border-strong);
}

.service-logo-box {
  width: 54px;
  height: 54px;
  border-radius: 14px;
  background: #1c1c24;
  border: 1px solid var(--border-medium);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--accent-white);
  font-weight: 800;
  font-size: 20px;
}

.service-name {
  font-size: 16px;
  font-weight: 700;
  color: var(--text-primary);
}

.service-status-tag {
  font-size: 12px;
  padding: 3px 8px;
  border-radius: var(--radius-pill);
  background: var(--bg-elevated);
  color: var(--text-secondary);
  border: 1px solid var(--border-subtle);
}

.service-disclaimer-box {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-md);
  padding: 20px 24px;
  font-size: 13px;
  color: var(--text-muted);
  line-height: 1.7;
  display: flex;
  gap: 16px;
  align-items: flex-start;
}

.disclaimer-icon {
  font-size: 18px;
  color: var(--text-primary);
  flex-shrink: 0;
  margin-top: 1px;
}

/* ==========================================================================
   套餐方案 Pricing Section
   ========================================================================== */
.pricing-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 22px;
  align-items: stretch;
}

.pricing-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 32px 24px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  position: relative;
  transition: all var(--transition-normal);
}

.pricing-card:hover {
  border-color: var(--border-strong);
  transform: translateY(-4px);
}

.pricing-card.featured {
  background: var(--bg-tertiary);
  border: 1px solid var(--accent-white);
  box-shadow: var(--shadow-elevated), var(--glow-light);
}

.card-ribbon {
  position: absolute;
  top: -12px;
  left: 50%;
  transform: translateX(-50%);
  background: #ffffff;
  color: #000000;
  font-size: 11px;
  font-weight: 800;
  padding: 4px 12px;
  border-radius: var(--radius-pill);
  letter-spacing: 0.04em;
  text-transform: uppercase;
  white-space: nowrap;
}

.plan-header {
  margin-bottom: 24px;
}

.plan-title {
  font-size: 20px;
  font-weight: 800;
  color: var(--text-primary);
  margin-bottom: 6px;
}

.plan-desc {
  font-size: 13px;
  color: var(--text-muted);
}

.plan-price-wrap {
  display: flex;
  align-items: baseline;
  gap: 4px;
  margin: 20px 0;
}

.price-currency {
  font-size: 20px;
  font-weight: 700;
  color: var(--text-primary);
}

.price-amount {
  font-size: 42px;
  font-weight: 900;
  letter-spacing: -0.03em;
  color: var(--text-primary);
}

.price-period {
  font-size: 14px;
  color: var(--text-muted);
}

.plan-features-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 13px;
  margin-bottom: 30px;
  font-size: 14px;
  color: var(--text-secondary);
}

.plan-feature-item {
  display: flex;
  align-items: center;
  gap: 10px;
}

.check-icon {
  width: 16px;
  height: 16px;
  color: var(--accent-white);
  flex-shrink: 0;
}

.pricing-disclaimer {
  text-align: center;
  font-size: 13px;
  color: var(--text-muted);
  margin-top: 36px;
}

/* ==========================================================================
   常见问题 FAQ Section
   ========================================================================== */
.faq-list {
  display: flex;
  flex-direction: column;
  gap: 14px;
  max-width: 820px;
  margin: 0 auto;
}

.faq-item {
  background: var(--bg-secondary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.faq-item:hover {
  border-color: var(--border-medium);
}

.faq-question {
  width: 100%;
  background: none;
  border: none;
  padding: 22px 26px;
  text-align: left;
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
  color: var(--text-primary);
  font-size: 17px;
  font-weight: 700;
  gap: 16px;
}

.faq-icon {
  width: 20px;
  height: 20px;
  transition: transform var(--transition-fast);
  color: var(--text-muted);
  flex-shrink: 0;
}

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

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease-out;
  color: var(--text-muted);
  font-size: 14.5px;
  line-height: 1.7;
}

.faq-item.open .faq-answer {
  max-height: 500px;
}

.faq-answer-inner {
  padding: 0 26px 24px 26px;
  border-top: 1px solid var(--border-subtle);
  margin-top: 4px;
  padding-top: 16px;
}

/* ==========================================================================
   知识科普导读 Knowledge Preview Section
   ========================================================================== */
.articles-preview-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  margin-bottom: 36px;
}

.article-card-preview {
  background: var(--bg-secondary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 26px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 18px;
  transition: all var(--transition-normal);
  text-decoration: none;
}

.article-card-preview:hover {
  border-color: var(--border-strong);
  background: var(--bg-tertiary);
  transform: translateY(-3px);
}

.article-meta-row {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 12px;
  color: var(--text-muted);
}

.article-preview-title {
  font-size: 18px;
  font-weight: 700;
  color: var(--text-primary);
  line-height: 1.4;
}

.article-preview-desc {
  font-size: 14px;
  color: var(--text-muted);
  line-height: 1.6;
}

.article-read-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 13px;
  font-weight: 600;
  color: var(--accent-white);
}

/* ==========================================================================
   CTA 召集令 Banner
   ========================================================================== */
.cta-banner-section {
  padding: 80px 0;
  text-align: center;
}

.cta-banner-box {
  background: linear-gradient(180deg, #18181f 0%, #111114 100%);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-lg);
  padding: 60px 32px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 22px;
}

.cta-title {
  font-size: clamp(26px, 3.5vw, 38px);
  font-weight: 800;
  color: var(--accent-white);
}

.cta-desc {
  font-size: 16px;
  color: var(--text-muted);
  max-width: 600px;
}

/* ==========================================================================
   页脚 Footer (严守 4 个入口要求)
   ========================================================================== */
.site-footer {
  background-color: var(--bg-primary);
  border-top: 1px solid var(--border-subtle);
  padding: 60px 0 40px 0;
  color: var(--text-muted);
  font-size: 14px;
}

.footer-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 24px;
  padding-bottom: 36px;
  border-bottom: 1px solid var(--border-subtle);
}

.footer-brand-summary {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.footer-logo-title {
  font-size: 20px;
  font-weight: 900;
  color: var(--accent-white);
}

.footer-links-group {
  display: flex;
  align-items: center;
  gap: 28px;
  list-style: none;
}

.footer-link-item a {
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  transition: color var(--transition-fast);
}

.footer-link-item a:hover {
  color: var(--accent-white);
  text-decoration: underline;
  text-underline-offset: 4px;
}

.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 16px;
  padding-top: 28px;
  font-size: 13px;
  color: var(--text-disabled);
}

.footer-disclaimer-note {
  max-width: 620px;
  line-height: 1.6;
}

/* ==========================================================================
   浮动章节跳转控制器 (页面右侧上一章/下一章箭头)
   ========================================================================== */
.chapter-nav-floating {
  position: fixed;
  right: 24px;
  top: 50%;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: 12px;
  z-index: 95;
  background: rgba(18, 18, 22, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  padding: 10px 8px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--border-medium);
  box-shadow: var(--shadow-subtle);
}

.chapter-nav-btn {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  color: var(--text-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.chapter-nav-btn:hover:not(:disabled) {
  background: var(--accent-white);
  color: var(--text-inverse);
  transform: scale(1.08);
}

.chapter-nav-btn:disabled {
  opacity: 0.25;
  cursor: not-allowed;
  pointer-events: none;
}

.chapter-nav-btn svg {
  width: 18px;
  height: 18px;
}

/* ==========================================================================
   响应式断点适配 (移动端优先与流式收缩)
   ========================================================================== */
@media (max-width: 1080px) {
  .features-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .pricing-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .streaming-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .articles-preview-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 860px) {
  .hero-layout {
    grid-template-columns: 1fr;
    gap: 40px;
  }

  .hero-interactive-card {
    order: 2;
  }

  .nav-desktop,
  .header-cta-desktop {
    display: none;
  }

  .mobile-menu-toggle {
    display: block;
  }

  .footer-top {
    flex-direction: column;
    align-items: flex-start;
  }

  .footer-links-group {
    flex-wrap: wrap;
    gap: 18px;
  }
}

@media (max-width: 640px) {
  .page-section {
    padding: 64px 0;
  }

  .section-title {
    font-size: 28px;
  }

  .features-grid,
  .pricing-grid,
  .streaming-grid,
  .articles-preview-grid {
    grid-template-columns: 1fr;
  }

  .hero-metrics {
    gap: 20px;
    flex-wrap: wrap;
  }

  .hero-cta-group {
    flex-direction: column;
    width: 100%;
  }

  .hero-cta-group .btn {
    width: 100%;
  }

  /* 移动端章节导航停靠在右下角，避免遮挡正文 */
  .chapter-nav-floating {
    right: 14px;
    top: auto;
    bottom: 24px;
    transform: none;
    flex-direction: row;
    padding: 6px 8px;
    gap: 8px;
  }

  .chapter-nav-btn {
    width: 36px;
    height: 36px;
  }

  .footer-bottom {
    flex-direction: column;
    align-items: flex-start;
  }
}

/* 动效克制与减弱动画 */
@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;
  }
}