/* DeepThinking AI Landing Page — style.css
   Design tokens, reset, components, page layouts */

/* ─── Reset ─── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body { font-family: var(--font-sans); font-size: 16px; line-height: 1.6; color: var(--text); background: var(--bg); -webkit-font-smoothing: antialiased; }
img, svg { display: block; max-width: 100%; }
a { color: inherit; text-decoration: none; }
button { font: inherit; cursor: pointer; border: none; background: none; }
ul, ol { list-style: none; }

/* ─── Design Tokens ─── */
:root {
  /* Primary (indigo) */
  --primary: #4f46e5;
  --primary-hover: #4338ca;
  --primary-light: #eef2ff;
  --primary-ring: #c7d2fe;
  --primary-50: #eef2ff;
  --primary-100: #e0e7ff;
  --primary-500: #6366f1;
  --primary-600: #4f46e5;
  --primary-700: #4338ca;
  --primary-800: #3730a3;
  --primary-900: #312e81;

  /* Neutrals */
  --bg: #f6f7f9;
  --surface: #fff;
  --surface-alt: #fafbfc;
  --text: #0f172a;
  --text-sec: #64748b;
  --text-mut: #94a3b8;
  --border: #e7e9ee;
  --border-strong: #d7dbe3;

  /* Accents */
  --success: #10b981;
  --danger: #ef4444;

  /* Geometry */
  --radius: 9px;
  --radius-lg: 14px;
  --radius-sm: 6px;
  --radius-xl: 20px;

  /* Font */
  --font-sans: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --font-mono: ui-monospace, "SF Mono", Menlo, monospace;

  /* Spacing scale */
  --sp-1: 4px;
  --sp-2: 8px;
  --sp-3: 12px;
  --sp-4: 16px;
  --sp-5: 20px;
  --sp-6: 24px;
  --sp-8: 32px;
  --sp-10: 40px;
  --sp-12: 48px;
  --sp-16: 64px;
  --sp-20: 80px;
  --sp-24: 96px;

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
  --shadow: 0 1px 3px rgba(0,0,0,0.08), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 6px rgba(0,0,0,0.06), 0 2px 4px rgba(0,0,0,0.04);
  --shadow-lg: 0 10px 15px rgba(0,0,0,0.08), 0 4px 6px rgba(0,0,0,0.04);
  --shadow-xl: 0 20px 25px rgba(0,0,0,0.1), 0 8px 10px rgba(0,0,0,0.04);

  /* Transitions */
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --duration: 200ms;
}

/* ─── Typography ─── */
h1, h2, h3, h4, h5, h6 { font-weight: 700; line-height: 1.2; color: var(--text); }
h1 { font-size: clamp(2.25rem, 5vw, 3.5rem); letter-spacing: -0.025em; }
h2 { font-size: clamp(1.75rem, 4vw, 2.5rem); letter-spacing: -0.02em; }
h3 { font-size: clamp(1.25rem, 2.5vw, 1.5rem); }
p { color: var(--text-sec); }
.text-gradient {
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-500) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ─── Layout ─── */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--sp-6);
}
.section {
  padding: var(--sp-20) 0;
}
.section-sm {
  padding: var(--sp-16) 0;
}

/* ─── Navbar ─── */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid transparent;
  transition: border-color var(--duration) var(--ease), box-shadow var(--duration) var(--ease);
}
.navbar.scrolled {
  border-bottom-color: var(--border);
  box-shadow: var(--shadow-sm);
}
.navbar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}
.navbar-logo {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  font-weight: 700;
  font-size: 1.125rem;
  color: var(--text);
}
.navbar-logo svg {
  width: 32px;
  height: 32px;
}
.navbar-links {
  display: flex;
  align-items: center;
  gap: var(--sp-8);
}
.navbar-links a {
  font-size: 0.9375rem;
  font-weight: 500;
  color: var(--text-sec);
  transition: color var(--duration) var(--ease);
}
.navbar-links a:hover {
  color: var(--text);
}
.navbar-actions {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
}
.navbar-hamburger {
  display: none;
  width: 40px;
  height: 40px;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius);
}
.navbar-hamburger span {
  display: block;
  width: 20px;
  height: 2px;
  background: var(--text);
  position: relative;
  transition: background var(--duration) var(--ease);
}
.navbar-hamburger span::before,
.navbar-hamburger span::after {
  content: '';
  position: absolute;
  width: 20px;
  height: 2px;
  background: var(--text);
  transition: transform var(--duration) var(--ease);
}
.navbar-hamburger span::before { top: -6px; }
.navbar-hamburger span::after { top: 6px; }
.navbar-hamburger.active span { background: transparent; }
.navbar-hamburger.active span::before { transform: rotate(45deg); top: 0; }
.navbar-hamburger.active span::after { transform: rotate(-45deg); top: 0; }

/* Mobile nav */
.mobile-nav {
  display: none;
  position: fixed;
  top: 64px;
  left: 0;
  right: 0;
  bottom: 0;
  background: var(--surface);
  padding: var(--sp-6);
  flex-direction: column;
  gap: var(--sp-4);
  z-index: 999;
}
.mobile-nav.open { display: flex; }
.mobile-nav a {
  font-size: 1.125rem;
  font-weight: 500;
  padding: var(--sp-3) 0;
  color: var(--text-sec);
  border-bottom: 1px solid var(--border);
}
.mobile-nav a:hover { color: var(--text); }

/* ─── Buttons ─── */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-2);
  padding: 10px 20px;
  font-size: 0.9375rem;
  font-weight: 600;
  border-radius: var(--radius);
  transition: all var(--duration) var(--ease);
  white-space: nowrap;
}
.btn-primary {
  background: var(--primary);
  color: #fff;
  box-shadow: 0 1px 2px rgba(79, 70, 229, 0.3);
}
.btn-primary:hover {
  background: var(--primary-hover);
  box-shadow: 0 4px 12px rgba(79, 70, 229, 0.3);
  transform: translateY(-1px);
}
.btn-secondary {
  background: var(--surface);
  color: var(--text);
  border: 1px solid var(--border-strong);
}
.btn-secondary:hover {
  background: var(--bg);
  border-color: var(--text-mut);
}
.btn-ghost {
  color: var(--text-sec);
  padding: 8px 16px;
}
.btn-ghost:hover {
  color: var(--text);
  background: var(--bg);
}
.btn-lg {
  padding: 14px 28px;
  font-size: 1rem;
  border-radius: var(--radius-lg);
}
.btn-sm {
  padding: 6px 14px;
  font-size: 0.8125rem;
}

/* ─── Cards ─── */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--sp-8);
  transition: box-shadow var(--duration) var(--ease), transform var(--duration) var(--ease);
}
.card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}
.card-icon {
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius);
  background: var(--primary-light);
  color: var(--primary);
  margin-bottom: var(--sp-5);
}
.card-icon svg { width: 24px; height: 24px; }
.card h3 { margin-bottom: var(--sp-3); }
.card p { font-size: 0.9375rem; }

/* ─── Hero ─── */
.hero {
  padding: calc(64px + var(--sp-20)) 0 var(--sp-20);
  text-align: center;
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: '';
  position: absolute;
  top: -200px;
  left: 50%;
  transform: translateX(-50%);
  width: 800px;
  height: 800px;
  background: radial-gradient(ellipse at center, rgba(79, 70, 229, 0.08) 0%, transparent 70%);
  pointer-events: none;
}
.hero-content {
  position: relative;
  z-index: 1;
  max-width: 720px;
  margin: 0 auto;
}
.hero h1 {
  margin-bottom: var(--sp-5);
}
.hero p {
  font-size: clamp(1.0625rem, 2vw, 1.25rem);
  max-width: 560px;
  margin: 0 auto var(--sp-8);
}
.hero-actions {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-4);
  flex-wrap: wrap;
}

/* ─── Models Strip ─── */
.models-strip {
  text-align: center;
  padding: var(--sp-12) 0;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}
.models-strip p {
  font-size: 0.875rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-mut);
  margin-bottom: var(--sp-6);
}
.models-grid {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-10);
  flex-wrap: wrap;
}
.model-badge {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  font-size: 1.0625rem;
  font-weight: 600;
  color: var(--text-sec);
}
.model-badge svg { width: 24px; height: 24px; }

/* ─── Features Grid ─── */
.features { text-align: center; }
.features h2 { margin-bottom: var(--sp-3); }
.features > .container > p { max-width: 560px; margin: 0 auto var(--sp-12); }
.features-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-6);
}

/* ─── Steps / How It Works ─── */
.steps { text-align: center; background: var(--surface); }
.steps h2 { margin-bottom: var(--sp-3); }
.steps > .container > p { max-width: 500px; margin: 0 auto var(--sp-12); }
.steps-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-8);
}
.step {
  position: relative;
  text-align: center;
}
.step-number {
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto var(--sp-5);
  border-radius: 50%;
  background: var(--primary);
  color: #fff;
  font-size: 1.25rem;
  font-weight: 700;
}
.step h3 { margin-bottom: var(--sp-2); }
.step p { font-size: 0.9375rem; }

/* ─── CTA Banner ─── */
.cta-banner {
  background: linear-gradient(135deg, var(--primary-900) 0%, var(--primary-700) 100%);
  border-radius: var(--radius-xl);
  padding: var(--sp-16) var(--sp-8);
  text-align: center;
  color: #fff;
}
.cta-banner h2 { color: #fff; margin-bottom: var(--sp-4); }
.cta-banner p { color: rgba(255,255,255,0.8); margin-bottom: var(--sp-8); max-width: 500px; margin-left: auto; margin-right: auto; }
.cta-banner .btn-primary {
  background: #fff;
  color: var(--primary);
  box-shadow: 0 2px 8px rgba(0,0,0,0.15);
}
.cta-banner .btn-primary:hover {
  background: var(--primary-50);
  transform: translateY(-1px);
}

/* ─── Footer ─── */
.footer {
  background: var(--surface);
  border-top: 1px solid var(--border);
  padding: var(--sp-12) 0 var(--sp-8);
}
.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: var(--sp-10);
  margin-bottom: var(--sp-10);
}
.footer-brand p {
  font-size: 0.875rem;
  margin-top: var(--sp-3);
  max-width: 280px;
}
.footer-col h4 {
  font-size: 0.8125rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-mut);
  margin-bottom: var(--sp-4);
}
.footer-col a {
  display: block;
  font-size: 0.9375rem;
  color: var(--text-sec);
  padding: var(--sp-1) 0;
  transition: color var(--duration) var(--ease);
}
.footer-col a:hover { color: var(--primary); }
.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: var(--sp-8);
  border-top: 1px solid var(--border);
  font-size: 0.8125rem;
  color: var(--text-mut);
}

/* ─── Pricing Page ─── */
.pricing-header {
  text-align: center;
  padding: calc(64px + var(--sp-16)) 0 var(--sp-12);
}
.pricing-header h1 { margin-bottom: var(--sp-4); }
.pricing-header p { max-width: 520px; margin: 0 auto; }

/* Billing toggle */
.billing-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-3);
  margin: var(--sp-8) 0 var(--sp-10);
}
.billing-toggle span {
  font-size: 0.9375rem;
  font-weight: 500;
  color: var(--text-sec);
}
.billing-toggle span.active { color: var(--text); }
.toggle-switch {
  position: relative;
  width: 44px;
  height: 24px;
  background: var(--border-strong);
  border-radius: 12px;
  cursor: pointer;
  transition: background var(--duration) var(--ease);
}
.toggle-switch.active { background: var(--primary); }
.toggle-switch::after {
  content: '';
  position: absolute;
  top: 2px;
  left: 2px;
  width: 20px;
  height: 20px;
  background: #fff;
  border-radius: 50%;
  box-shadow: var(--shadow-sm);
  transition: transform var(--duration) var(--ease);
}
.toggle-switch.active::after { transform: translateX(20px); }
.billing-save {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--success);
  background: rgba(16, 185, 129, 0.1);
  padding: 2px 8px;
  border-radius: 10px;
}

/* Pricing cards */
.pricing-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-6);
  margin-bottom: var(--sp-16);
}
.pricing-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--sp-8);
  display: flex;
  flex-direction: column;
}
.pricing-card.featured {
  border-color: var(--primary);
  box-shadow: 0 0 0 1px var(--primary), var(--shadow-lg);
  position: relative;
}
.pricing-card.featured::before {
  content: 'Most Popular';
  position: absolute;
  top: -12px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--primary);
  color: #fff;
  font-size: 0.75rem;
  font-weight: 600;
  padding: 4px 12px;
  border-radius: 10px;
}
.pricing-card-header {
  margin-bottom: var(--sp-6);
  padding-bottom: var(--sp-6);
  border-bottom: 1px solid var(--border);
}
.pricing-card-header h3 { margin-bottom: var(--sp-2); font-size: 1.25rem; }
.pricing-card-header p { font-size: 0.875rem; }
.pricing-amount {
  display: flex;
  align-items: baseline;
  gap: var(--sp-1);
  margin-top: var(--sp-4);
}
.pricing-amount .price {
  font-size: 2.5rem;
  font-weight: 800;
  color: var(--text);
  letter-spacing: -0.02em;
}
.pricing-amount .period {
  font-size: 0.9375rem;
  color: var(--text-mut);
}
.pricing-features {
  flex: 1;
  margin-bottom: var(--sp-6);
}
.pricing-features li {
  display: flex;
  align-items: flex-start;
  gap: var(--sp-3);
  padding: var(--sp-2) 0;
  font-size: 0.9375rem;
  color: var(--text-sec);
}
.pricing-features li svg {
  width: 18px;
  height: 18px;
  color: var(--success);
  flex-shrink: 0;
  margin-top: 2px;
}
.pricing-card .btn { width: 100%; }

/* Model pricing table */
.model-pricing {
  margin-bottom: var(--sp-16);
}
.model-pricing h2 {
  text-align: center;
  margin-bottom: var(--sp-3);
}
.model-pricing > p {
  text-align: center;
  margin-bottom: var(--sp-8);
}
.pricing-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--surface);
  border-radius: var(--radius-lg);
  overflow: hidden;
  border: 1px solid var(--border);
}
.pricing-table th,
.pricing-table td {
  padding: var(--sp-4) var(--sp-5);
  text-align: left;
  font-size: 0.9375rem;
}
.pricing-table th {
  background: var(--bg);
  font-weight: 600;
  color: var(--text);
  font-size: 0.8125rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.pricing-table td {
  border-top: 1px solid var(--border);
  color: var(--text-sec);
}
.pricing-table tr:hover td { background: var(--surface-alt); }
.pricing-table .provider {
  font-weight: 600;
  color: var(--text);
}

/* FAQ */
.faq { margin-bottom: var(--sp-16); }
.faq h2 { text-align: center; margin-bottom: var(--sp-8); }
.faq-item {
  border-bottom: 1px solid var(--border);
}
.faq-question {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  padding: var(--sp-5) 0;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text);
  text-align: left;
}
.faq-question svg {
  width: 20px;
  height: 20px;
  color: var(--text-mut);
  transition: transform var(--duration) var(--ease);
}
.faq-item.open .faq-question svg { transform: rotate(180deg); }
.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 300ms var(--ease);
}
.faq-item.open .faq-answer { max-height: 200px; }
.faq-answer p {
  padding-bottom: var(--sp-5);
  font-size: 0.9375rem;
}

/* ─── About Page ─── */
.about-hero {
  padding: calc(64px + var(--sp-16)) 0 var(--sp-12);
  text-align: center;
}
.about-hero h1 { margin-bottom: var(--sp-4); }
.about-hero p { max-width: 600px; margin: 0 auto; font-size: 1.125rem; }
.values-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-6);
}

/* ─── Contact Page ─── */
.contact-hero {
  padding: calc(64px + var(--sp-16)) 0 var(--sp-12);
  text-align: center;
}
.contact-hero h1 { margin-bottom: var(--sp-4); }
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--sp-10);
}
.contact-form {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--sp-8);
}
.form-group {
  margin-bottom: var(--sp-5);
}
.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: var(--sp-2);
}
.form-group input,
.form-group textarea,
.form-group select {
  width: 100%;
  padding: 10px 14px;
  font-size: 0.9375rem;
  font-family: var(--font-sans);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text);
  transition: border-color var(--duration) var(--ease), box-shadow var(--duration) var(--ease);
}
.form-group input:focus,
.form-group textarea:focus,
.form-group select:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}
.form-group textarea { resize: vertical; min-height: 120px; }
.contact-info {
  display: flex;
  flex-direction: column;
  gap: var(--sp-6);
}
.contact-info-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--sp-6);
}
.contact-info-card h3 { font-size: 1rem; margin-bottom: var(--sp-2); }
.contact-info-card p { font-size: 0.9375rem; }
.contact-info-card a { color: var(--primary); font-weight: 500; }
.contact-info-card a:hover { text-decoration: underline; }

/* ─── Checkout Page ─── */
.checkout-container {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--sp-6);
}
.checkout-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: var(--sp-12);
  text-align: center;
  max-width: 480px;
  width: 100%;
  box-shadow: var(--shadow-lg);
}
.checkout-spinner {
  width: 48px;
  height: 48px;
  border: 4px solid var(--border);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  margin: 0 auto var(--sp-6);
}
@keyframes spin { to { transform: rotate(360deg); } }
.checkout-success { color: var(--success); }
.checkout-success svg { width: 64px; height: 64px; margin: 0 auto var(--sp-4); }
.checkout-error { color: var(--danger); }

/* ─── Responsive ─── */
@media (max-width: 1024px) {
  .features-grid,
  .steps-grid,
  .pricing-grid,
  .values-grid { grid-template-columns: repeat(2, 1fr); }
  .footer-grid { grid-template-columns: 1fr 1fr; gap: var(--sp-8); }
}

@media (max-width: 768px) {
  body { font-size: 15px; }
  .navbar-links, .navbar-actions { display: none; }
  .navbar-hamburger { display: flex; }
  .section { padding: var(--sp-16) 0; }
  .hero { padding: calc(64px + var(--sp-12)) 0 var(--sp-12); }
  .features-grid,
  .steps-grid,
  .pricing-grid,
  .values-grid { grid-template-columns: 1fr; }
  .contact-grid { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr; }
  .hero-actions { flex-direction: column; }
  .models-grid { gap: var(--sp-6); }
  .pricing-card.featured { margin-top: var(--sp-4); }
  .cta-banner { padding: var(--sp-10) var(--sp-6); border-radius: var(--radius-lg); }
}

/* ─── Legal Pages ─── */
.legal-content h2 { margin-top: var(--sp-12); margin-bottom: var(--sp-4); font-size: 1.25rem; }
.legal-content h3 { margin-top: var(--sp-8); margin-bottom: var(--sp-3); font-size: 1.1rem; }
.legal-content p { margin-bottom: var(--sp-4); line-height: 1.7; color: var(--text-sec); }
.legal-content ul { margin-bottom: var(--sp-4); padding-left: var(--sp-6); list-style: disc; }
.legal-content li { margin-bottom: var(--sp-2); line-height: 1.6; color: var(--text-sec); }
.legal-content a { color: var(--primary); font-weight: 500; }
.legal-content a:hover { text-decoration: underline; }