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

:root {
  --primary: #1a73e8;
  --primaryLight: #e8f0fe;
  --secondary: #333;
  --bg: #fff;
  --text: #333;
  --lightText: #666;
  --border: #e0e0e0;
}

body {
  font-family: Lato, Arial, Helvetica, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

header {
  background: var(--primary);
  color: #fff;
  padding: 1rem 2rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

header .logo-icon {
  width: 40px;
  height: 40px;
  background: rgba(255,255,255,0.2);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1.2rem;
}

header a {
  color: #fff;
  text-decoration: none;
  font-size: 1.3rem;
  font-weight: 700;
}

nav {
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
  overflow-x: auto;
}

nav ul {
  list-style: none;
  display: flex;
  gap: 0;
  padding: 0 1rem;
  max-width: 1100px;
  margin: 0 auto;
}

nav ul li a {
  display: block;
  padding: 0.75rem 1rem;
  text-decoration: none;
  color: var(--text);
  font-size: 0.9rem;
  white-space: nowrap;
  border-bottom: 3px solid transparent;
  transition: border-color 0.2s;
}

nav ul li a:hover {
  border-bottom-color: var(--primary);
  background: var(--primaryLight);
}

nav ul li a.active {
  border-bottom-color: var(--primary);
  color: var(--primary);
  font-weight: 700;
}

main {
  max-width: 900px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
}

main h1 {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 1.5rem;
  color: var(--primary);
}

main h2 {
  font-size: 1.4rem;
  margin: 1.5rem 0 0.75rem;
  color: var(--secondary);
}

main h3 {
  font-size: 1.1rem;
  margin: 1rem 0 0.5rem;
  color: var(--secondary);
}

main p {
  margin-bottom: 1rem;
}

main ul, main ol {
  margin: 0.5rem 0 1rem 1.5rem;
}

main li {
  margin-bottom: 0.4rem;
}

main a {
  color: var(--primary);
  text-decoration: none;
}

main a:hover {
  text-decoration: underline;
}

main img {
  max-width: 100%;
  height: auto;
  margin: 1rem 0;
  border-radius: 4px;
}

.footer-book {
  background: #f8f9fa;
  border-top: 1px solid var(--border);
  padding: 2rem 1.5rem;
  display: flex;
  gap: 1.5rem;
  max-width: 900px;
  margin: 2rem auto;
  border-radius: 8px;
}

.footer-book-image {
  flex-shrink: 0;
}

.footer-book-image img {
  width: 120px;
  height: auto;
  border-radius: 4px;
}

.footer-book-content {
  flex: 1;
}

.footer-book-content h3 {
  font-size: 1rem;
  margin-bottom: 0.5rem;
}

.footer-book-content h3 a {
  color: var(--primary);
  text-decoration: none;
}

.footer-book-content small {
  display: block;
  color: var(--lightText);
  font-size: 0.85rem;
  margin-bottom: 0.3rem;
}

@media (max-width: 768px) {
  header {
    padding: 0.75rem 1rem;
  }

  header a {
    font-size: 1.1rem;
  }

  nav ul {
    padding: 0 0.5rem;
  }

  nav ul li a {
    padding: 0.6rem 0.75rem;
    font-size: 0.8rem;
  }

  main {
    padding: 1.5rem 1rem;
  }

  main h1 {
    font-size: 1.5rem;
  }

  .footer-book {
    flex-direction: column;
    align-items: center;
    text-align: center;
    margin: 1.5rem 1rem;
  }

  .footer-book-image img {
    width: 100px;
  }
}