:root {
  --navy: #0d1321;
  --navy-light: #1a2332;
  --teal: #14b8a6;
  --purple: #a78bfa;
  --orange: #f59e0b;
  --white: #f8fafc;
  --gray: #94a3b8;
  --gray-dark: #64748b;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
  background: var(--navy);
  color: var(--white);
  line-height: 1.6;
}

.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 24px;
}

h1, h2, h3 {
  line-height: 1.2;
}

h2 {
  font-size: 2rem;
  margin-bottom: 1.5rem;
}

h3 {
  font-size: 1.25rem;
  margin-bottom: 0.75rem;
}

a {
  color: var(--teal);
}

/* Hero */
.hero {
  padding: 80px 0;
  background: linear-gradient(180deg, var(--navy-light) 0%, var(--navy) 100%);
}

.hero-content {
  display: flex;
  align-items: center;
  gap: 60px;
}

.hero-text {
  flex: 1;
}

.hero h1 {
  font-size: 3.5rem;
  margin-bottom: 0.5rem;
}

.hero h1 .teal {
  color: var(--teal);
}

.hero h1 .purple {
  color: var(--purple);
}

.subtitle {
  font-size: 1.5rem;
  color: var(--white);
  margin-bottom: 1rem;
  padding-bottom: 0.75rem;
  border-bottom: 3px solid var(--orange);
  display: inline-block;
}

.tagline {
  font-size: 1.25rem;
  color: var(--gray);
  margin-bottom: 2rem;
}

.hero-cover img {
  border-radius: 8px;
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.4);
}

/* Buttons */
.btn {
  display: inline-block;
  padding: 14px 28px;
  border-radius: 6px;
  text-decoration: none;
  font-weight: 600;
  font-size: 1rem;
  transition: transform 0.2s, box-shadow 0.2s;
}

.btn:hover {
  transform: translateY(-2px);
}

.btn-primary {
  background: var(--teal);
  color: var(--navy);
}

.btn-primary:hover {
  box-shadow: 0 8px 20px rgba(20, 184, 166, 0.3);
}

.btn-secondary {
  background: transparent;
  border: 2px solid var(--purple);
  color: var(--purple);
}

.btn-secondary:hover {
  background: var(--purple);
  color: var(--navy);
}

.btn-large {
  padding: 18px 40px;
  font-size: 1.125rem;
}

.cta-buttons {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
}

/* Sections */
section {
  padding: 80px 0;
}

section:nth-child(even) {
  background: var(--navy-light);
}

/* Problem */
.problem p {
  font-size: 1.125rem;
  margin-bottom: 1rem;
  max-width: 700px;
}

.problem strong {
  color: var(--teal);
}

/* Features */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 32px;
}

.feature {
  padding: 24px;
  background: var(--navy);
  border-radius: 8px;
  border-left: 3px solid var(--purple);
}

.feature h3 {
  color: var(--teal);
}

.feature p {
  color: var(--gray);
}

/* TOC */
.toc-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 32px;
  margin-bottom: 32px;
}

.toc-section {
  background: var(--navy);
  padding: 24px;
  border-radius: 8px;
}

.toc-section h3 {
  color: var(--purple);
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--gray-dark);
}

.toc-section ol {
  list-style-position: inside;
  color: var(--gray);
}

.toc-section li {
  padding: 4px 0;
}

.appendices {
  background: var(--navy);
  padding: 24px;
  border-radius: 8px;
  max-width: 400px;
}

.appendices h3 {
  color: var(--orange);
  margin-bottom: 1rem;
}

.appendices ul {
  list-style: none;
  color: var(--gray);
}

.appendices li {
  padding: 4px 0;
}

/* Audience */
.audience-list {
  list-style: none;
  margin-bottom: 1.5rem;
}

.audience-list li {
  padding: 8px 0;
  padding-left: 24px;
  position: relative;
}

.audience-list li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 16px;
  width: 8px;
  height: 8px;
  background: var(--teal);
  border-radius: 50%;
}

/* Math */
.math p {
  font-size: 1.125rem;
  margin-bottom: 1rem;
  max-width: 600px;
}

.math strong {
  color: var(--orange);
}

/* Buy */
.buy {
  text-align: center;
}

.what-you-get {
  display: inline-block;
  text-align: left;
  margin-bottom: 2rem;
}

.what-you-get ul {
  list-style: none;
}

.what-you-get li {
  padding: 8px 0;
  padding-left: 28px;
  position: relative;
  font-size: 1.125rem;
}

.what-you-get li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 14px;
  width: 16px;
  height: 16px;
  background: var(--teal);
  border-radius: 50%;
}

.price-box {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.price {
  font-size: 3rem;
  font-weight: 700;
  color: var(--white);
}

/* Footer */
footer {
  padding: 40px 0;
  text-align: center;
  color: var(--gray-dark);
  border-top: 1px solid var(--navy-light);
}

/* Sample page */
.sample-header {
  padding: 40px 0;
  background: var(--navy-light);
}

.sample-header .back-link {
  display: inline-block;
  margin-bottom: 1rem;
  color: var(--gray);
  text-decoration: none;
}

.sample-header .back-link:hover {
  color: var(--teal);
}

.sample-content {
  padding: 60px 0;
}

.sample-content h1 {
  font-size: 2.5rem;
  margin-bottom: 1.5rem;
  color: var(--purple);
}

.sample-content h2 {
  font-size: 1.5rem;
  margin-top: 3rem;
  margin-bottom: 1rem;
  color: var(--teal);
}

.sample-content h3 {
  margin-top: 2rem;
  color: var(--white);
}

.sample-content p {
  margin-bottom: 1rem;
  max-width: 700px;
}

.sample-content ul, .sample-content ol {
  margin-bottom: 1rem;
  margin-left: 1.5rem;
}

.sample-content li {
  margin-bottom: 0.5rem;
}

.sample-content pre {
  background: #1e293b;
  padding: 20px;
  border-radius: 8px;
  overflow-x: auto;
  margin-bottom: 1.5rem;
  border-left: 3px solid var(--purple);
}

.sample-content code {
  font-family: 'Fira Code', 'Consolas', monospace;
  font-size: 0.9rem;
  color: #e2e8f0;
}

.sample-content p code {
  background: #1e293b;
  padding: 2px 6px;
  border-radius: 4px;
}

.sample-content strong {
  color: var(--teal);
}

.sample-cta {
  margin-top: 60px;
  padding-top: 40px;
  border-top: 1px solid var(--gray-dark);
  text-align: center;
}

.sample-cta p {
  max-width: none;
  margin-bottom: 1.5rem;
  font-size: 1.25rem;
}

/* Responsive */
@media (max-width: 768px) {
  .hero {
    padding: 60px 0;
  }

  .hero-content {
    flex-direction: column-reverse;
    text-align: center;
  }

  .hero h1 {
    font-size: 2.5rem;
  }

  .subtitle {
    font-size: 1.25rem;
  }

  .cta-buttons {
    justify-content: center;
  }

  .hero-cover img {
    width: 200px;
  }

  section {
    padding: 60px 0;
  }

  h2 {
    font-size: 1.75rem;
  }
}