/* Reset and Base Styles */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --primary-color: #4078c0;
  --text-color: #333;
  --text-secondary: #666;
  --border-color: #e1e4e8;
  --bg-light: #f6f8fa;
  --sidebar-width: 280px;
  --top-nav-height: 60px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  line-height: 1.6;
  color: var(--text-color);
  background: white;
}

/* Top Navigation Bar */
.top-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--top-nav-height);
  background: white;
  border-bottom: 1px solid var(--border-color);
  z-index: 1000;
  box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.nav-container {
  max-width: 1400px;
  margin: 0 auto;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 20px;
}

.nav-brand a {
  font-size: 24px;
  font-weight: 700;
  color: var(--primary-color);
  text-decoration: none;
  transition: opacity 0.2s;
}

.nav-brand a:hover {
  opacity: 0.8;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 20px;
}

.nav-links a {
  color: var(--text-color);
  text-decoration: none;
  font-weight: 500;
  transition: color 0.2s;
}

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

.nav-toggle {
  display: none;
  background: var(--primary-color);
  color: white;
  border: none;
  padding: 8px 16px;
  border-radius: 6px;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.2s;
}

.nav-toggle:hover {
  background: #3568a6;
}

/* Book Container */
.book-container {
  display: flex;
  margin-top: var(--top-nav-height);
  min-height: calc(100vh - var(--top-nav-height));
}

/* Sidebar */
.sidebar {
  position: fixed;
  left: 0;
  top: var(--top-nav-height);
  width: var(--sidebar-width);
  height: calc(100vh - var(--top-nav-height));
  background: var(--bg-light);
  border-right: 1px solid var(--border-color);
  overflow-y: auto;
  z-index: 100;
}

.sidebar-header {
  display: none; /* Hidden on desktop */
  padding: 20px;
  border-bottom: 1px solid var(--border-color);
  background: white;
  position: sticky;
  top: 0;
  z-index: 10;
}

.sidebar-header h2 {
  font-size: 20px;
  margin: 0;
}

.sidebar-close {
  display: none;
  position: absolute;
  top: 20px;
  right: 20px;
  background: none;
  border: none;
  font-size: 32px;
  line-height: 1;
  color: var(--text-secondary);
  cursor: pointer;
  padding: 0;
  width: 32px;
  height: 32px;
}

.chapter-nav {
  padding: 20px;
}

.chapter-link {
  display: block;
  padding: 10px 15px;
  margin-bottom: 4px;
  color: var(--text-color);
  text-decoration: none;
  border-radius: 6px;
  transition: all 0.2s;
  font-size: 14px;
}

.chapter-link:hover {
  background: white;
  color: var(--primary-color);
}

.chapter-link.active {
  background: var(--primary-color);
  color: white;
  font-weight: 600;
}

/* Main Content */
.main-content {
  flex: 1;
  margin-left: var(--sidebar-width);
  min-height: calc(100vh - var(--top-nav-height));
  display: flex;
  flex-direction: column;
}

.book-content {
  flex: 1;
  max-width: 900px;
  margin: 0 auto;
  padding: 40px 60px;
  width: 100%;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  margin-top: 24px;
  margin-bottom: 16px;
  font-weight: 600;
  line-height: 1.25;
}

h1 {
  font-size: 2.5em;
  border-bottom: 2px solid var(--border-color);
  padding-bottom: 0.3em;
  margin-bottom: 24px;
}

h2 {
  font-size: 1.8em;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 0.3em;
}

h3 {
  font-size: 1.4em;
}

p {
  margin-bottom: 16px;
}

ul, ol {
  margin-bottom: 16px;
  padding-left: 2em;
}

li {
  margin-bottom: 8px;
}

/* Code blocks */
pre {
  background: var(--bg-light);
  border: 1px solid var(--border-color);
  border-radius: 6px;
  padding: 16px;
  overflow-x: auto;
  margin-bottom: 16px;
  font-size: 14px;
  line-height: 1.6;
}

code {
  background: var(--bg-light);
  padding: 2px 6px;
  border-radius: 3px;
  font-size: 90%;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, Courier, monospace;
}

pre code {
  background: transparent;
  padding: 0;
  border-radius: 0;
  font-size: inherit;
}

/* Blockquotes */
blockquote {
  padding: 0 1em;
  color: var(--text-secondary);
  border-left: 4px solid var(--border-color);
  margin: 0 0 16px 0;
  font-style: italic;
}

/* Links */
a {
  color: var(--primary-color);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

/* Page Navigation (Prev/Next) */
.page-navigation {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 60px;
  padding-top: 30px;
  border-top: 2px solid var(--border-color);
  gap: 20px;
}

.page-navigation .prev,
.page-navigation .next {
  flex: 1;
}

.page-navigation .prev {
  text-align: left;
}

.page-navigation .next {
  text-align: right;
}

.page-navigation a {
  display: inline-block;
  padding: 12px 24px;
  background: var(--bg-light);
  border: 1px solid var(--border-color);
  border-radius: 6px;
  color: var(--text-color);
  text-decoration: none;
  font-weight: 500;
  transition: all 0.2s;
}

.page-navigation a:hover {
  background: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
  text-decoration: none;
}

/* Footer */
.page-footer {
  margin-top: 60px;
  padding: 30px 60px;
  background: var(--bg-light);
  border-top: 1px solid var(--border-color);
  text-align: center;
  color: var(--text-secondary);
  font-size: 14px;
}

.page-footer p {
  margin: 5px 0;
}

/* Sidebar Overlay (Mobile) */
.sidebar-overlay {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0, 0, 0, 0.5);
  z-index: 99;
  opacity: 0;
  transition: opacity 0.3s;
}

.sidebar-overlay.active {
  display: block;
  opacity: 1;
}

/* Responsive Design */
@media screen and (max-width: 768px) {
  .nav-toggle {
    display: block;
  }

  .sidebar {
    transform: translateX(-100%);
    transition: transform 0.3s ease;
    width: 85%;
    max-width: 320px;
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .sidebar-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
  }

  .sidebar-close {
    display: block;
  }

  .main-content {
    margin-left: 0;
  }

  .book-content {
    padding: 30px 20px;
  }

  .page-footer {
    padding: 20px;
  }

  h1 {
    font-size: 2em;
  }

  h2 {
    font-size: 1.5em;
  }

  .page-navigation {
    flex-direction: column;
  }

  .page-navigation .prev,
  .page-navigation .next {
    width: 100%;
    text-align: center;
  }

  .page-navigation a {
    display: block;
    width: 100%;
  }
}

@media screen and (min-width: 769px) and (max-width: 1200px) {
  .book-content {
    padding: 40px 40px;
  }
}

/* Smooth scrolling */
html {
  scroll-behavior: smooth;
}

/* Custom scrollbar for sidebar */
.sidebar::-webkit-scrollbar {
  width: 8px;
}

.sidebar::-webkit-scrollbar-track {
  background: transparent;
}

.sidebar::-webkit-scrollbar-thumb {
  background: #ccc;
  border-radius: 4px;
}

.sidebar::-webkit-scrollbar-thumb:hover {
  background: #999;
}