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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  line-height: 1.6;
  color: #333;
  background: #fff;
  padding: 20px;
  max-width: 800px;
  margin: 0 auto;
}

h1 {
  font-size: 2rem;
  margin-bottom: 1.5rem;
  line-height: 1.3;
}

h2 {
  font-size: 1.5rem;
  margin-top: 3rem;
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid #eee;
}

h3 {
  font-size: 1.2rem;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
}

h4 {
  font-size: 1.1rem;
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
  font-weight: 600;
}

p {
  margin-bottom: 1rem;
}

strong {
  font-weight: 600;
}

ul, ol {
  margin: 1rem 0 1rem 1.5rem;
}

li {
  margin-bottom: 0.5rem;
}

.intro {
  background: #f8f9fa;
  padding: 1.5rem;
  border-left: 4px solid #333;
  margin: 2rem 0;
}

/* Главное оглавление */
.main-toc {
  background: #f8f9fa;
  padding: 2rem;
  margin: 2rem 0;
  border-radius: 4px;
}

.main-toc h2 {
  margin-top: 0;
  border: none;
  font-size: 1.5rem;
  margin-bottom: 1.5rem;
}

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

.main-toc-list > li {
  margin: 1.5rem 0;
  padding: 1rem;
  background: white;
  border-radius: 4px;
  border-left: 3px solid #666;
}

.main-toc-list > li > a {
  text-decoration: none;
  color: #333;
  font-size: 1.2rem;
  font-weight: 600;
  display: block;
  margin-bottom: 0.5rem;
}

.main-toc-list > li > a:hover {
  color: #000;
}

.main-toc-desc {
  color: #666;
  font-size: 0.95rem;
  line-height: 1.5;
}

/* Навигационные кнопки */
.nav-buttons {
  display: flex;
  gap: 1rem;
  margin: 2rem 0;
  padding: 1rem 0;
  border-top: 1px solid #eee;
  border-bottom: 1px solid #eee;
}

.nav-button {
  padding: 0.5rem 1rem;
  background: #f8f9fa;
  border: 1px solid #ddd;
  border-radius: 4px;
  text-decoration: none;
  color: #333;
  font-size: 0.9rem;
}

.nav-button:hover {
  background: #e9ecef;
}

/* Блоки для разных типов контента */
.example {
  border-left: 3px solid #666;
  padding-left: 1rem;
  margin: 1.5rem 0;
  color: #555;
}

.key {
  font-weight: 600;
  color: #333;
  margin: 1rem 0;
  padding: 1rem;
  background: #fff9e6;
  border-radius: 4px;
}

/* Таблицы */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.95rem;
}

th, td {
  padding: 0.75rem;
  text-align: left;
  border: 1px solid #ddd;
}

th {
  background: #f8f9fa;
  font-weight: 600;
}

hr {
  border: none;
  border-top: 1px solid #eee;
  margin: 3rem 0;
}

/* Стили для рабочей тетради курса */
.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 20px;
}

.page-header {
  text-align: center;
  margin-bottom: 3rem;
  padding-bottom: 2rem;
  border-bottom: 2px solid #e0e0e0;
}

.page-header h1 {
  margin-bottom: 0.5rem;
  color: #2c3e50;
}

.subtitle {
  font-size: 1.1rem;
  color: #666;
  margin: 0;
}

.intro-section {
  margin-bottom: 3rem;
}

.info-box {
  background: #f8f9fa;
  padding: 1.5rem;
  border-radius: 8px;
  border-left: 4px solid #0066cc;
}

.info-box ul {
  margin: 0.5rem 0 0 0;
  padding-left: 1.5rem;
}

.info-box li {
  margin: 0.5rem 0;
}

.blocks-navigation h2 {
  margin-bottom: 2rem;
  color: #2c3e50;
}

.block-card {
  background: white;
  border: 1px solid #e0e0e0;
  border-radius: 8px;
  padding: 1.5rem;
  margin-bottom: 1.5rem;
  transition: box-shadow 0.2s;
}

.block-card:hover {
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.block-card.disabled {
  opacity: 0.6;
  background: #f5f5f5;
}

.block-number {
  display: inline-block;
  background: #0066cc;
  color: white;
  padding: 0.25rem 0.75rem;
  border-radius: 4px;
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: 0.75rem;
}

.block-card h3 {
  margin: 0.5rem 0;
  color: #2c3e50;
}

.block-card p {
  color: #666;
  margin: 0.75rem 0;
  line-height: 1.6;
}

.block-link {
  display: inline-block;
  color: #0066cc;
  text-decoration: none;
  font-weight: 600;
  margin-top: 0.5rem;
}

.block-link:hover {
  text-decoration: underline;
}

.block-status {
  display: inline-block;
  color: #999;
  font-style: italic;
  margin-top: 0.5rem;
}

.page-footer {
  text-align: center;
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 1px solid #e0e0e0;
  color: #666;
  font-size: 0.9rem;
}

/* Промо-блок */
.promo-block {
  background: #f0f7ff;
  padding: 2rem;
  margin: 2rem 0;
  border-radius: 8px;
  border-left: 4px solid #0066cc;
}

.promo-block h2 {
  margin-top: 0;
  border: none;
  color: #0066cc;
}

.promo-block h3 {
  margin-top: 1.5rem;
  color: #333;
}

.promo-block ul {
  margin: 1rem 0;
}

.promo-link {
  display: inline-block;
  padding: 0.75rem 1.5rem;
  background: #0066cc;
  color: white;
  text-decoration: none;
  border-radius: 4px;
  margin-top: 1rem;
  font-weight: 600;
}

.promo-link:hover {
  background: #0052a3;
}

/* Адаптивность */
@media (max-width: 768px) {
  body {
    padding: 15px;
  }

  h1 {
    font-size: 1.5rem;
  }

  h2 {
    font-size: 1.3rem;
  }

  h3 {
    font-size: 1.1rem;
  }

  .nav-buttons {
    flex-direction: column;
  }

  .promo-block {
    padding: 1.5rem;
  }
  
  .container {
    padding: 10px;
  }
  
  .page-header {
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
  }
  
  .block-card {
    padding: 1rem;
  }
}