/* ==========================================================================
   云图加速器 (Yuntu Accelerator) - Light Theme Modern CSS
   Pure CSS3, Zero External JS/CSS Framework Dependencies
   ========================================================================== */

:root {
  --bg-main: #f8fafc;
  --bg-surface: #ffffff;
  --bg-subtle: #f1f5f9;
  --bg-accent-light: #eff6ff;
  
  --text-main: #0f172a;
  --text-muted: #475569;
  --text-light: #64748b;
  --text-white: #ffffff;

  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-gradient: linear-gradient(135deg, #2563eb 0%, #1d4ed8 100%);
  --accent: #0284c7;
  --accent-gradient: linear-gradient(135deg, #38bdf8 0%, #2563eb 100%);
  --success: #10b981;
  --badge-bg: #dbeafe;
  --badge-text: #1e40af;

  --border-color: #e2e8f0;
  --border-hover: #cbd5e1;

  --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.06);
  --shadow-md: 0 4px 12px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 12px 24px rgba(15, 23, 42, 0.1);
  --shadow-xl: 0 20px 32px rgba(15, 23, 42, 0.12);

  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 24px;
  --radius-pill: 9999px;

  --max-width: 1200px;
  --transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
  scroll-behavior: smooth;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif;
  background-color: var(--bg-main);
  color: var(--text-main);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: var(--transition);
}

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

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

.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* Typography Helpers */
.text-center { text-align: center; }
.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 16px;
  border-radius: var(--radius-pill);
  background-color: var(--badge-bg);
  color: var(--badge-text);
  font-size: 0.875rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  margin-bottom: 16px;
  border: 1px solid rgba(37, 99, 235, 0.15);
}

.section-title {
  font-size: 2.25rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text-main);
  margin-bottom: 12px;
  line-height: 1.25;
}

.section-subtitle {
  font-size: 1.125rem;
  color: var(--text-muted);
  max-width: 680px;
  margin: 0 auto 48px auto;
}

/* Button Component */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 14px 28px;
  font-size: 1rem;
  font-weight: 700;
  border-radius: var(--radius-md);
  cursor: pointer;
  border: 2px solid transparent;
  transition: var(--transition);
  min-height: 48px;
  white-space: nowrap;
}

.btn-primary {
  background: var(--primary-gradient);
  color: var(--text-white);
  box-shadow: 0 4px 14px rgba(37, 99, 235, 0.35);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(37, 99, 235, 0.45);
  color: var(--text-white);
}

.btn-secondary {
  background-color: var(--bg-surface);
  color: var(--text-main);
  border-color: var(--border-color);
  box-shadow: var(--shadow-sm);
}

.btn-secondary:hover {
  background-color: var(--bg-subtle);
  border-color: var(--border-hover);
  color: var(--primary);
  transform: translateY(-2px);
}

.btn-block {
  width: 100%;
}

.btn-lg {
  padding: 16px 36px;
  font-size: 1.125rem;
  border-radius: var(--radius-md);
}

/* Navbar */
.navbar {
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
}

.navbar .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 76px;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--text-main);
  letter-spacing: -0.01em;
}

.brand-icon {
  width: 38px;
  height: 38px;
  background: var(--primary-gradient);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 32px;
  list-style: none;
}

.nav-links a {
  color: var(--text-muted);
  font-weight: 600;
  font-size: 0.95rem;
}

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

.nav-actions {
  display: flex;
  align-items: center;
  gap: 16px;
}

/* Hero Section */
.hero {
  padding: 80px 0 60px 0;
  position: relative;
  overflow: hidden;
  background: radial-gradient(circle at 50% 0%, rgba(37, 99, 235, 0.08) 0%, rgba(248, 250, 252, 0) 70%);
}

.hero-content {
  max-width: 860px;
  margin: 0 auto;
  text-align: center;
}

.hero-title {
  font-size: 3.25rem;
  font-weight: 900;
  line-height: 1.15;
  letter-spacing: -0.03em;
  color: var(--text-main);
  margin-bottom: 20px;
}

.hero-title .gradient-text {
  background: var(--primary-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-desc {
  font-size: 1.25rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin-bottom: 36px;
  max-width: 720px;
  margin-left: auto;
  margin-right: auto;
}

.hero-cta {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  margin-bottom: 50px;
}

.hero-stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
  background-color: var(--bg-surface);
  padding: 24px;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-md);
  margin-top: 40px;
}

.stat-item {
  text-align: center;
}

.stat-number {
  font-size: 2rem;
  font-weight: 800;
  color: var(--primary);
  line-height: 1.2;
}

.stat-label {
  font-size: 0.875rem;
  color: var(--text-muted);
  font-weight: 600;
  margin-top: 4px;
}

/* Features Section */
.features {
  padding: 90px 0;
  background-color: var(--bg-main);
}

.features-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
}

.feature-card {
  background-color: var(--bg-surface);
  border-radius: var(--radius-md);
  padding: 32px;
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
  transition: var(--transition);
}

.feature-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: rgba(37, 99, 235, 0.3);
}

.feature-icon {
  width: 52px;
  height: 52px;
  background-color: var(--bg-accent-light);
  color: var(--primary);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 20px;
}

.feature-title {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: 10px;
  color: var(--text-main);
}

.feature-desc {
  font-size: 0.975rem;
  color: var(--text-muted);
  line-height: 1.6;
}

/* Ecosystem Section (Streaming & AI) */
.ecosystem {
  padding: 90px 0;
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border-color);
  border-bottom: 1px solid var(--border-color);
}

.eco-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 32px;
}

.eco-card {
  background-color: var(--bg-main);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 36px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

.eco-header {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  margin-bottom: 20px;
}

.eco-tag {
  padding: 4px 12px;
  background-color: rgba(37, 99, 235, 0.1);
  color: var(--primary);
  border-radius: var(--radius-pill);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
}

.eco-title {
  font-size: 1.4rem;
  font-weight: 800;
  margin-bottom: 8px;
}

.eco-desc {
  color: var(--text-muted);
  font-size: 0.95rem;
  margin-bottom: 24px;
}

.platform-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.platform-chip {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 14px;
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text-main);
  box-shadow: var(--shadow-sm);
}

/* Pricing Section */
.pricing {
  padding: 90px 0;
  background-color: var(--bg-main);
}

.pricing-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
  align-items: stretch;
}

.pricing-card {
  background-color: var(--bg-surface);
  border-radius: var(--radius-lg);
  padding: 36px 28px;
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  position: relative;
  transition: var(--transition);
}

.pricing-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-xl);
}

.pricing-card.popular {
  border: 2px solid var(--primary);
  box-shadow: var(--shadow-lg);
}

.popular-badge {
  position: absolute;
  top: -14px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--primary-gradient);
  color: white;
  padding: 4px 16px;
  border-radius: var(--radius-pill);
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.plan-name {
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--text-main);
  margin-bottom: 8px;
}

.plan-desc {
  font-size: 0.875rem;
  color: var(--text-light);
  margin-bottom: 24px;
  min-height: 40px;
}

.plan-price {
  margin-bottom: 24px;
  display: flex;
  align-items: baseline;
  gap: 4px;
}

.price-currency {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary);
}

.price-val {
  font-size: 3rem;
  font-weight: 900;
  color: var(--text-main);
  line-height: 1;
}

.price-period {
  font-size: 0.9rem;
  color: var(--text-muted);
}

.plan-features {
  list-style: none;
  margin-bottom: 32px;
  flex-grow: 1;
}

.plan-features li {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 0.925rem;
  color: var(--text-muted);
  margin-bottom: 12px;
}

.check-icon {
  width: 18px;
  height: 18px;
  background-color: rgba(16, 185, 129, 0.15);
  color: var(--success);
  border-radius: 50%;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 12px;
  font-weight: 900;
  flex-shrink: 0;
}

/* Reviews / Testimonials */
.reviews {
  padding: 90px 0;
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border-color);
}

.reviews-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
}

.review-card {
  background-color: var(--bg-main);
  padding: 28px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

.rating-stars {
  color: #f59e0b;
  font-size: 1.1rem;
  margin-bottom: 12px;
}

.review-content {
  font-size: 0.95rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin-bottom: 20px;
  font-style: italic;
}

.user-info {
  display: flex;
  align-items: center;
  gap: 12px;
}

.user-avatar {
  width: 42px;
  height: 42px;
  border-radius: 50%;
  background: var(--primary-gradient);
  color: white;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
}

.user-name {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-main);
}

.user-role {
  font-size: 0.8rem;
  color: var(--text-light);
}

/* FAQ Accordion Section */
.faq {
  padding: 90px 0;
  background-color: var(--bg-main);
}

.faq-container {
  max-width: 800px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.faq-item {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}

.faq-item details {
  width: 100%;
}

.faq-item summary {
  padding: 20px 24px;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-main);
  cursor: pointer;
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  user-select: none;
  transition: var(--transition);
}

.faq-item summary::-webkit-details-marker {
  display: none;
}

.faq-item summary::after {
  content: "+";
  font-size: 1.4rem;
  font-weight: 400;
  color: var(--primary);
  transition: transform 0.2s ease;
}

.faq-item details[open] summary::after {
  content: "−";
  transform: rotate(180deg);
}

.faq-item details[open] summary {
  background-color: var(--bg-accent-light);
  color: var(--primary);
  border-bottom: 1px solid var(--border-color);
}

.faq-answer {
  padding: 20px 24px;
  font-size: 0.975rem;
  color: var(--text-muted);
  line-height: 1.7;
}

/* Footer Section - STRICT REQUIREMENT: Only 4 Headings/Links */
.footer {
  background-color: #0f172a;
  color: #94a3b8;
  padding: 50px 0 40px 0;
  border-top: 1px solid #1e293b;
  margin-top: auto;
}

.footer-nav {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 40px;
  flex-wrap: wrap;
  margin-bottom: 30px;
}

.footer-nav-item {
  font-size: 1.05rem;
  font-weight: 700;
  color: #f8fafc;
  transition: var(--transition);
  padding: 6px 12px;
  border-radius: var(--radius-sm);
}

.footer-nav-item:hover {
  color: #38bdf8;
  background-color: rgba(255, 255, 255, 0.05);
}

.footer-copyright {
  text-align: center;
  font-size: 0.875rem;
  color: #64748b;
  border-top: 1px solid #1e293b;
  padding-top: 24px;
}

/* Secondary Page Wrapper (About, Terms, Privacy, Sitemap) */
.page-header {
  padding: 60px 0 40px 0;
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  margin-bottom: 50px;
}

.page-title {
  font-size: 2.5rem;
  font-weight: 800;
  margin-bottom: 12px;
}

.page-desc {
  font-size: 1.1rem;
  color: var(--text-muted);
}

.page-body {
  padding-bottom: 80px;
}

.content-box {
  background-color: var(--bg-surface);
  border-radius: var(--radius-lg);
  padding: 40px;
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
  max-width: 920px;
  margin: 0 auto;
}

.content-box h2 {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-main);
  margin: 32px 0 16px 0;
  border-bottom: 2px solid var(--bg-subtle);
  padding-bottom: 8px;
}

.content-box h2:first-child {
  margin-top: 0;
}

.content-box p {
  color: var(--text-muted);
  line-height: 1.7;
  margin-bottom: 16px;
  font-size: 1rem;
}

.content-box ul {
  margin: 0 0 20px 24px;
  color: var(--text-muted);
}

.content-box li {
  margin-bottom: 8px;
  line-height: 1.6;
}

/* Node Grid inside About page */
.node-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
  margin-top: 20px;
}

.node-card {
  background-color: var(--bg-main);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 16px;
  text-align: center;
}

.node-name {
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 4px;
}

.node-detail {
  font-size: 0.85rem;
  color: var(--text-light);
}

/* RESPONSIVE MEDIA QUERIES (Mobile-first optimization) */
@media (max-width: 1024px) {
  .features-grid, .pricing-grid, .reviews-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 768px) {
  .container {
    padding: 0 16px;
  }
  
  .navbar .container {
    height: 64px;
  }
  
  .nav-links {
    display: none; /* Mobile optimization: focused CTA */
  }

  .hero {
    padding: 40px 0;
  }

  .hero-title {
    font-size: 2.2rem;
  }

  .hero-desc {
    font-size: 1rem;
  }

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

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

  .hero-stats {
    grid-template-columns: repeat(2, 1fr);
    gap: 16px;
  }

  .features-grid, .eco-grid, .pricing-grid, .reviews-grid, .node-grid {
    grid-template-columns: 1fr;
  }

  .pricing-card.popular {
    transform: none;
  }

  .footer-nav {
    flex-direction: column;
    gap: 16px;
    align-items: center;
  }

  .content-box {
    padding: 24px 18px;
  }

  .page-title {
    font-size: 1.8rem;
  }
}