:root {
  --primary: #7c3aed;
  --primary-dark: #5b21b6;
  --secondary: #f59e0b;
  --dark: #1f2937;
  --light: #f3f4f6;
  --white: #ffffff;
  --text: #374151;
  --border: #e5e7eb;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', sans-serif;
  line-height: 1.7;
  color: var(--text);
  background: var(--white);
}

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Navigation */
.topnav {
  background: var(--white);
  border-bottom: 2px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 1000;
  box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.topnav .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 20px;
}

.topnav .logo {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--primary);
  text-decoration: none;
}

.topnav .nav-links {
  display: flex;
  gap: 2rem;
  align-items: center;
}

.topnav .nav-links a {
  text-decoration: none;
  color: var(--text);
  font-weight: 500;
  transition: colour 0.3s;
}

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

.download-btn {
  background: var(--primary);
  color: var(--white) !important;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  font-weight: 600;
}

.download-btn:hover {
  background: var(--primary-dark);
}

/* Material Content */
main {
  padding: 3rem 0;
}

.material-content {
  background: var(--white);
}

.material-header {
  margin-bottom: 3rem;
  padding-bottom: 2rem;
  border-bottom: 3px solid var(--primary);
  position: relative;
  z-index: 1;
}

.material-header h1 {
  font-size: 2.5rem;
  color: var(--dark);
  margin-bottom: 1rem;
}

.material-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--text);
  font-size: 0.95rem;
  flex-wrap: wrap;
  gap: 1rem;
}

.btn-primary {
  display: inline-block;
  background: var(--primary);
  color: var(--white);
  padding: 0.75rem 1.5rem;
  border-radius: 6px;
  text-decoration: none;
  font-weight: 600;
  transition: background 0.3s;
}

.btn-primary:hover {
  background: var(--primary-dark);
}

.btn-secondary {
  display: inline-block;
  background: var(--secondary);
  color: var(--white);
  padding: 0.75rem 1.5rem;
  border-radius: 6px;
  text-decoration: none;
  font-weight: 600;
  transition: background 0.3s;
}

.btn-secondary:hover {
  background: #d97706;
}

/* Table of Contents */
.toc {
  background: var(--light);
  padding: 1.5rem;
  border-radius: 8px;
  border-left: 4px solid var(--primary);
  margin-bottom: 3rem;
}

.toc h2 {
  font-size: 1.25rem;
  margin-bottom: 1rem;
  color: var(--primary);
}

.toc ul {
  list-style: none;
  padding-left: 0;
}

.toc li {
  margin: 0.5rem 0;
}

.toc a {
  color: var(--text);
  text-decoration: none;
}

.toc a:hover {
  color: var(--primary);
  text-decoration: underline;
}

/* Content */
.content {
  font-size: 1.1rem;
}

.content h1, .content h2, .content h3, .content h4 {
  color: var(--dark);
  margin-top: 2rem;
  margin-bottom: 1rem;
}

.content h1 {
  font-size: 2rem;
  border-bottom: 2px solid var(--primary);
  padding-bottom: 0.5rem;
}

.content h2 {
  font-size: 1.75rem;
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.5rem;
}

.content h3 {
  font-size: 1.5rem;
}

.content h4 {
  font-size: 1.25rem;
}

.content p {
  margin: 1rem 0;
}

.content ul, .content ol {
  margin: 1rem 0;
  padding-left: 2rem;
}

.content li {
  margin: 0.5rem 0;
}

.content table {
  width: 100%;
  border-collapse: collapse;
  margin: 2rem 0;
  font-size: 1rem;
}

.content th, .content td {
  border: 1px solid var(--border);
  padding: 0.75rem;
  text-align: left;
}

.content th {
  background: var(--primary);
  color: var(--white);
  font-weight: 600;
}

.content tr:nth-child(even) {
  background: var(--light);
}

.content blockquote {
  border-left: 4px solid var(--secondary);
  padding-left: 1.5rem;
  margin: 1.5rem 0;
  color: #555;
  font-style: italic;
}

.content code {
  background: var(--light);
  padding: 0.2rem 0.5rem;
  border-radius: 4px;
  font-family: 'Courier New', monospace;
  font-size: 0.9em;
}

.content pre {
  background: var(--dark);
  color: var(--white);
  padding: 1.5rem;
  border-radius: 8px;
  overflow-x: auto;
  margin: 1.5rem 0;
}

.content pre code {
  background: transparent;
  color: var(--white);
  padding: 0;
}

.content hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2rem 0;
}

/* Material Footer */
.material-footer {
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
  text-align: center;
}

.material-footer a {
  color: var(--primary);
  text-decoration: none;
  font-weight: 600;
}

.material-footer a:hover {
  text-decoration: underline;
}

/* Site Footer */
.site-footer {
  background: var(--dark);
  color: var(--white);
  padding: 3rem 0;
  text-align: center;
  margin-top: 4rem;
}

.site-footer a {
  color: var(--secondary);
  text-decoration: none;
}

.site-footer a:hover {
  text-decoration: underline;
}

/* Materials Index */
.materials-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 2rem;
  margin: 3rem 0;
}

.material-card {
  background: var(--white);
  border: 2px solid var(--border);
  border-radius: 12px;
  padding: 2rem;
  transition: transform 0.3s, box-shadow 0.3s, border-colour 0.3s;
}

.material-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 12px 24px rgba(0,0,0,0.1);
  border-color: var(--primary);
}

.material-card h3 {
  color: var(--primary);
  font-size: 1.5rem;
  margin-bottom: 1rem;
}

.material-card p {
  color: var(--text);
  margin-bottom: 1.5rem;
}

.material-card .actions {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

.material-category {
  margin-bottom: 4rem;
}

.material-category h2 {
  font-size: 2rem;
  color: var(--dark);
  margin-bottom: 1.5rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--primary);
}

.protected-badge {
  display: inline-block;
  background: #e74c3c;
  color: white;
  padding: 0.25rem 0.75rem;
  border-radius: 4px;
  font-size: 0.85rem;
  font-weight: 600;
  margin-left: 0.5rem;
}

/* Responsive */
@media (max-width: 768px) {
  .topnav .nav-links {
    gap: 1rem;
  }

  .topnav .nav-links a:not(.download-btn) {
    display: none;
  }

  .material-header h1 {
    font-size: 2rem;
  }

  .material-meta {
    flex-direction: column;
    align-items: flex-start;
    gap: 1rem;
  }

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

  .material-card .actions {
    flex-direction: column;
  }

  .content {
    font-size: 1rem;
  }

  .content table {
    font-size: 0.9rem;
  }
}