/* ============================================
   ChinaAI / 中智AI — Brand Site Stylesheet
   Modern, clean, responsive design
   ============================================ */

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

:root {
  /* Brand Colors */
  --color-primary: #1a365d;
  --color-primary-light: #234a7d;
  --color-primary-dark: #112540;
  --color-accent: #d4a853;
  --color-accent-light: #e8c96a;
  --color-accent-dark: #b8923a;

  /* Neutrals */
  --color-white: #ffffff;
  --color-bg: #f8f9fb;
  --color-bg-alt: #edf0f3;
  --color-text: #1a202c;
  --color-text-secondary: #4a5568;
  --color-text-muted: #718096;
  --color-border: #e2e8f0;
  --color-border-light: #edf2f7;

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.07), 0 2px 4px -1px rgba(0,0,0,0.04);
  --shadow-lg: 0 10px 25px -3px rgba(0,0,0,0.08), 0 4px 6px -2px rgba(0,0,0,0.04);
  --shadow-xl: 0 20px 40px -5px rgba(0,0,0,0.1);

  /* Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;

  /* Transitions */
  --transition-base: 0.2s ease;
  --transition-smooth: 0.3s cubic-bezier(0.4, 0, 0.2, 1);

  /* Layout */
  --max-width: 1200px;
  --header-height: 68px;
}

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

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  color: var(--color-text);
  background: var(--color-white);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }
ul { list-style: none; }

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

.section {
  padding: 96px 0;
}

.section__title {
  font-size: clamp(1.75rem, 3.5vw, 2.5rem);
  font-weight: 800;
  text-align: center;
  color: var(--color-primary);
  margin-bottom: 16px;
  letter-spacing: -0.02em;
  line-height: 1.2;
}

.section__subtitle {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  text-align: center;
  max-width: 640px;
  margin: 0 auto 56px;
  line-height: 1.6;
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 28px;
  font-size: 1rem;
  font-weight: 600;
  border-radius: var(--radius-md);
  border: 2px solid transparent;
  cursor: pointer;
  transition: all var(--transition-smooth);
  white-space: nowrap;
  text-align: center;
}

.btn--primary {
  background: var(--color-accent);
  color: var(--color-primary-dark);
  border-color: var(--color-accent);
}
.btn--primary:hover {
  background: var(--color-accent-light);
  border-color: var(--color-accent-light);
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(212, 168, 83, 0.35);
}

.btn--outline {
  background: transparent;
  color: var(--color-primary);
  border-color: var(--color-primary);
}
.btn--outline:hover {
  background: var(--color-primary);
  color: var(--color-white);
  transform: translateY(-1px);
}

.btn--lg {
  padding: 16px 36px;
  font-size: 1.1rem;
  border-radius: var(--radius-lg);
}

.btn--full {
  width: 100%;
}

/* ============================================
   Header / Navigation
   ============================================ */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border-light);
  height: var(--header-height);
}

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

.header__logo {
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--color-primary);
  letter-spacing: -0.02em;
  display: flex;
  align-items: center;
  gap: 8px;
}

.header__nav {
  display: flex;
  gap: 4px;
}

.header__nav-link {
  padding: 8px 14px;
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  border-radius: var(--radius-sm);
  transition: all var(--transition-base);
}
.header__nav-link:hover {
  color: var(--color-primary);
  background: var(--color-bg);
}

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

/* --- Language Switcher --- */
.lang-switcher {
  position: relative;
}

.lang-switcher__toggle {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 8px 12px;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text);
  transition: all var(--transition-base);
}
.lang-switcher__toggle:hover {
  border-color: var(--color-accent);
  background: var(--color-white);
}

.lang-switcher__dropdown {
  display: none;
  position: absolute;
  top: calc(100% + 4px);
  right: 0;
  background: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  min-width: 160px;
  padding: 6px;
  z-index: 1001;
}
.lang-switcher__dropdown.active { display: block; }
.lang-switcher__dropdown button {
  display: block;
  width: 100%;
  padding: 10px 14px;
  border: none;
  background: none;
  text-align: left;
  cursor: pointer;
  font-size: 0.925rem;
  color: var(--color-text);
  border-radius: var(--radius-sm);
  transition: all var(--transition-base);
}
.lang-switcher__dropdown button:hover {
  background: var(--color-bg);
  color: var(--color-primary);
}
.lang-switcher__dropdown button.active {
  background: var(--color-primary);
  color: var(--color-white);
}

/* --- Mobile Menu Button --- */
.header__menu-btn {
  display: none;
  flex-direction: column;
  gap: 4px;
  padding: 8px;
  background: none;
  border: none;
  cursor: pointer;
}
.header__menu-btn span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--color-primary);
  border-radius: 1px;
  transition: all var(--transition-smooth);
}

/* ============================================
   Hero Section
   ============================================ */
.hero {
  padding: 140px 0 80px;
  text-align: center;
  background: linear-gradient(180deg, #f8f9fb 0%, #ffffff 100%);
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -20%;
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(212,168,83,0.08) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}
.hero::after {
  content: '';
  position: absolute;
  bottom: -30%;
  left: -15%;
  width: 500px;
  height: 500px;
  background: radial-gradient(circle, rgba(26,54,93,0.05) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

.hero .container { position: relative; z-index: 1; }

.hero__badge {
  display: inline-block;
  padding: 6px 18px;
  background: rgba(212, 168, 83, 0.12);
  color: var(--color-accent-dark);
  font-size: 0.85rem;
  font-weight: 600;
  border-radius: 100px;
  margin-bottom: 28px;
  letter-spacing: 0.01em;
}

.hero__title {
  font-size: clamp(2.25rem, 5vw, 3.75rem);
  font-weight: 800;
  color: var(--color-primary);
  line-height: 1.15;
  margin-bottom: 24px;
  letter-spacing: -0.03em;
}

.hero__subtitle {
  font-size: clamp(1rem, 1.5vw, 1.2rem);
  color: var(--color-text-secondary);
  max-width: 680px;
  margin: 0 auto 40px;
  line-height: 1.7;
}

.hero__cta-group {
  display: flex;
  justify-content: center;
  gap: 16px;
  margin-bottom: 60px;
  flex-wrap: wrap;
}

.hero__stats {
  display: flex;
  justify-content: center;
  gap: 48px;
  flex-wrap: wrap;
}

.hero__stat {
  text-align: center;
}
.hero__stat-num {
  display: block;
  font-size: 2.25rem;
  font-weight: 800;
  color: var(--color-accent);
  line-height: 1.2;
}
.hero__stat-label {
  font-size: 0.875rem;
  color: var(--color-text-muted);
}

/* ============================================
   Why Learn Section
   ============================================ */
.why { background: var(--color-white); }

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

.why__card {
  padding: 36px 28px;
  background: var(--color-bg);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-light);
  transition: all var(--transition-smooth);
}
.why__card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: transparent;
}

.why__card-icon {
  width: 56px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(212, 168, 83, 0.1);
  border-radius: var(--radius-md);
  margin-bottom: 20px;
}

.why__card-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: 12px;
}

.why__card-desc {
  font-size: 0.925rem;
  color: var(--color-text-secondary);
  line-height: 1.65;
  margin-bottom: 16px;
}

.why__card-data {
  font-size: 0.8rem;
  color: var(--color-accent-dark);
  font-weight: 500;
  padding-top: 12px;
  border-top: 1px solid var(--color-border);
}
.why__card-data strong {
  color: var(--color-accent);
  font-size: 1rem;
}

/* ============================================
   Courses Section
   ============================================ */
.courses { background: var(--color-bg); }

.courses__grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 24px;
}

.course-card {
  display: flex;
  flex-direction: column;
  padding: 32px 24px;
  background: var(--color-white);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-light);
  transition: all var(--transition-smooth);
  position: relative;
}
.course-card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-xl);
  border-color: transparent;
}

.course-card--popular {
  border: 2px solid var(--color-accent);
  background: linear-gradient(180deg, rgba(212,168,83,0.04), var(--color-white) 30%);
}

.course-card__badge {
  display: inline-block;
  padding: 4px 12px;
  font-size: 0.75rem;
  font-weight: 600;
  border-radius: 100px;
  margin-bottom: 16px;
  background: var(--color-bg);
  color: var(--color-text-secondary);
}
.course-card__badge--gold {
  background: var(--color-accent);
  color: var(--color-white);
}

.course-card__title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: 12px;
}

.course-card__price {
  font-size: 1.75rem;
  font-weight: 800;
  color: var(--color-primary);
  margin-bottom: 16px;
}

.course-card__desc {
  font-size: 0.85rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: 20px;
  flex-grow: 1;
}

.course-card__features {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 24px;
}
.course-card__features li {
  font-size: 0.85rem;
  color: var(--color-text-secondary);
  padding-left: 18px;
  position: relative;
}
.course-card__features li::before {
  content: '✓';
  position: absolute;
  left: 0;
  color: var(--color-accent);
  font-weight: 700;
  font-size: 0.8rem;
}

/* ============================================
   Free Toolkit Section
   ============================================ */
.toolkit { background: var(--color-primary); color: var(--color-white); }
.toolkit .section__title { color: var(--color-white); }
.toolkit .section__subtitle { color: rgba(255,255,255,0.7); }

.toolkit__steps {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  margin-bottom: 48px;
  flex-wrap: wrap;
}

.toolkit__step {
  text-align: center;
  padding: 32px 24px;
  max-width: 280px;
}
.toolkit__step-num {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 48px;
  height: 48px;
  margin: 0 auto 16px;
  border: 2px solid var(--color-accent);
  border-radius: 50%;
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--color-accent);
}
.toolkit__step h4 {
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: 8px;
}
.toolkit__step p {
  font-size: 0.875rem;
  color: rgba(255,255,255,0.65);
  line-height: 1.6;
}

.toolkit__step-arrow {
  display: flex;
  align-items: center;
  color: var(--color-accent);
}

.toolkit__cta-wrap { text-align: center; }

/* ============================================
   Stories Section
   ============================================ */
.stories { background: var(--color-white); }

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

.story-card {
  padding: 32px;
  background: var(--color-bg);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-light);
  transition: all var(--transition-smooth);
}
.story-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.story-card__avatar {
  width: 52px;
  height: 52px;
  border-radius: 50%;
  background: var(--color-primary);
  color: var(--color-white);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.95rem;
  margin-bottom: 16px;
}

.story-card__stars { color: var(--color-accent); margin-bottom: 8px; font-size: 0.9rem; }

.story-card__name {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: 4px;
}

.story-card__role {
  display: block;
  font-size: 0.8rem;
  color: var(--color-text-muted);
  margin-bottom: 16px;
}

.story-card__text {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
  font-style: italic;
}

/* ============================================
   Affiliate Section
   ============================================ */
.affiliate { background: var(--color-bg); }

.affiliate__grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
  margin-bottom: 48px;
}

.affiliate__card {
  padding: 36px 28px;
  text-align: center;
  background: var(--color-white);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-light);
  transition: all var(--transition-smooth);
}
.affiliate__card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.affiliate__card-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 16px;
}

.affiliate__card h4 {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: 10px;
}

.affiliate__card p {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
}

.affiliate__cta-wrap { text-align: center; }

/* ============================================
   FAQ Section
   ============================================ */
.faq { background: var(--color-white); }

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

.faq__item {
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  margin-bottom: 12px;
  overflow: hidden;
  transition: all var(--transition-smooth);
}
.faq__item[open] {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-md);
}

.faq__question {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px;
  cursor: pointer;
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-primary);
  list-style: none;
  user-select: none;
  transition: color var(--transition-base);
}
.faq__question::-webkit-details-marker { display: none; }
.faq__question::after {
  content: '+';
  flex-shrink: 0;
  width: 24px;
  height: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.3rem;
  color: var(--color-accent);
  transition: transform var(--transition-smooth);
}
.faq__item[open] .faq__question::after {
  content: '−';
  transform: rotate(180deg);
}
.faq__question:hover { color: var(--color-accent-dark); }

.faq__answer {
  padding: 0 24px 20px;
  font-size: 0.925rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
}

/* ============================================
   Footer
   ============================================ */
.footer {
  background: var(--color-primary-dark);
  color: rgba(255,255,255,0.7);
  padding: 64px 0 32px;
}

.footer__grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: 40px;
  margin-bottom: 48px;
}

.footer__logo {
  font-size: 1.3rem;
  font-weight: 800;
  color: var(--color-white);
  margin-bottom: 16px;
}

.footer__desc {
  font-size: 0.9rem;
  line-height: 1.6;
  margin-bottom: 20px;
  max-width: 320px;
}

.footer__social {
  display: flex;
  gap: 12px;
}

.footer__social-link {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 38px;
  height: 38px;
  border: 1px solid rgba(255,255,255,0.15);
  border-radius: var(--radius-sm);
  transition: all var(--transition-base);
}
.footer__social-link:hover {
  background: var(--color-accent);
  border-color: var(--color-accent);
  color: var(--color-primary-dark);
}

.footer__col h4 {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--color-white);
  margin-bottom: 16px;
}

.footer__col ul { display: flex; flex-direction: column; gap: 10px; }
.footer__col a {
  font-size: 0.875rem;
  transition: color var(--transition-base);
}
.footer__col a:hover { color: var(--color-accent); }

.footer__bottom {
  text-align: center;
  padding-top: 28px;
  border-top: 1px solid rgba(255,255,255,0.08);
  font-size: 0.825rem;
}

/* ============================================
   Responsive Design
   ============================================ */
@media (max-width: 1024px) {
  .why__grid,
  .stories__grid,
  .affiliate__grid { grid-template-columns: repeat(2, 1fr); }

  .courses__grid { grid-template-columns: repeat(3, 1fr); }

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

  .toolkit__step-arrow { display: none; }
}

@media (max-width: 768px) {
  .header__nav {
    display: none;
    position: fixed;
    top: var(--header-height);
    left: 0;
    right: 0;
    flex-direction: column;
    background: var(--color-white);
    padding: 16px;
    border-bottom: 1px solid var(--color-border);
    box-shadow: var(--shadow-lg);
  }
  .header__nav.active { display: flex; }

  .header__menu-btn { display: flex; }

  .header__nav-link { padding: 12px 16px; font-size: 1rem; }

  .section { padding: 64px 0; }

  .hero { padding: 120px 0 60px; }
  .hero__stats { gap: 24px; }

  .why__grid,
  .stories__grid,
  .affiliate__grid { grid-template-columns: 1fr; }

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

  .toolkit__steps { flex-direction: column; }

  .footer__grid { grid-template-columns: 1fr; gap: 32px; }

  .faq__question { padding: 16px 20px; font-size: 0.95rem; }
  .faq__answer { padding: 0 20px 16px; }
}

@media (max-width: 480px) {
  .hero__cta-group { flex-direction: column; align-items: center; }
  .hero__cta-group .btn { width: 100%; max-width: 320px; }

  .hero__stat-num { font-size: 1.75rem; }
  .hero__stat-label { font-size: 0.8rem; }

  .lang-switcher__dropdown { right: -40px; }
}