/* ==========================================================================
   ACADEMIC WEB READER - DESIGN SYSTEM & UI SPECIFICATION
   Strictly following DESIGN.md
   ========================================================================== */

:root {
  /* Surfaces & Backgrounds */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --bg-card: #ffffff;
  --bg-sidebar: #f8fafc;

  /* Text Colors */
  --text-main: #0f172a;       /* Slate 900 - High contrast body text */
  --text-muted: #475569;      /* Slate 600 - Secondary text */
  --text-subtle: #64748b;     /* Slate 500 - Captions, metadata, indices */

  /* Borders & Dividers */
  --border-color: #e2e8f0;    /* Slate 200 */
  --border-focus: #3b82f6;    /* Blue 500 */

  /* Primary Brand / Accent */
  --accent-primary: #2563eb;       /* Blue 600 */
  --accent-primary-hover: #1d4ed8; /* Blue 700 */
  --accent-light: #eff6ff;         /* Blue 50 */
  --accent-border: #bfdbfe;        /* Blue 200 */

  /* State & Alert Colors */
  --success-bg: #f0fdf4;
  --success-border: #bbf7d0;
  --success-text: #166534;

  --warning-bg: #fffbeb;
  --warning-border: #fde68a;
  --warning-text: #92400e;

  --danger-bg: #fef2f2;
  --danger-border: #fecaca;
  --danger-text: #991b1b;

  --info-bg: #f0f9ff;
  --info-border: #bae6fd;
  --info-text: #075985;

  /* Code & Syntax Colors (Academic High-Contrast Theme) */
  --code-inline-text: #0369a1;    /* Sky/Sapphire Blue 700 */
  --code-inline-bg: #f0f7ff;      /* Ice Blue Soft Tint */
  --code-inline-border: #bfdbfe;  /* Blue 200 */
  --code-block-bg: #0f172a;       /* Slate 900 */
  --code-header-bg: #1e293b;      /* Slate 800 */
  --code-border: #334155;         /* Slate 700 */

  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', Consolas, Monaco, 'Courier New', monospace;
  --font-serif: 'Charter', 'Bitstream Charter', 'Sitka Text', 'Cambria', Georgia, serif;

  /* Layout Spacing & Dimensions */
  --sidebar-width: 280px;
  --header-height: 64px;
  --content-max-width: 900px;

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;

  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);

  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-main);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

#reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  width: 0%;
  background: linear-gradient(90deg, var(--accent-primary), #60a5fa);
  z-index: 1000;
  transition: width 0.1s ease-out;
}

.app-layout {
  display: flex;
  min-height: 100vh;
}

/* Sidebar */
.sidebar {
  width: var(--sidebar-width);
  background-color: var(--bg-sidebar);
  border-right: 1px solid var(--border-color);
  position: fixed;
  top: 0;
  bottom: 0;
  left: 0;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  z-index: 50;
  transition: transform var(--transition-normal);
}

.sidebar-header {
  padding: 20px 24px;
  border-bottom: 1px solid var(--border-color);
  background: #ffffff;
}

.sidebar-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-main);
  letter-spacing: -0.01em;
  display: flex;
  align-items: center;
  gap: 8px;
  text-decoration: none;
}

.sidebar-title .logo-icon {
  font-size: 1.25rem;
}

.sidebar-subtitle {
  font-size: 0.8rem;
  color: var(--text-subtle);
  margin-top: 4px;
  font-weight: 500;
}

.sidebar-nav {
  padding: 16px 12px;
  flex: 1;
}

.nav-group-title {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-subtle);
  font-weight: 700;
  padding: 8px 12px 6px;
}

.nav-list {
  list-style: none;
}

.nav-item {
  margin-bottom: 2px;
}

.nav-link {
  display: flex;
  align-items: center;
  padding: 7px 10px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.84rem;
  font-weight: 500;
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
  gap: 10px;
  line-height: 1.3;
}

.nav-link:hover {
  background-color: var(--bg-tertiary);
  color: var(--text-main);
}

.nav-link.active {
  background-color: var(--accent-light);
  color: var(--accent-primary);
  font-weight: 600;
}

.nav-chapter-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 600;
  width: 24px;
  height: 20px;
  border-radius: 4px;
  background-color: #e2e8f0;
  color: var(--text-muted);
  flex-shrink: 0;
}

.nav-link.active .nav-chapter-num {
  background-color: var(--accent-primary);
  color: #ffffff;
}

.sidebar-toggle-btn {
  display: none;
  background: transparent;
  border: none;
  font-size: 1.25rem;
  cursor: pointer;
  color: var(--text-main);
  padding: 8px;
}

/* Main Content Area */
.main-wrapper {
  margin-left: var(--sidebar-width);
  flex: 1;
  display: flex;
  flex-direction: column;
  min-width: 0;
}

/* Header */
.top-header {
  height: var(--header-height);
  border-bottom: 1px solid var(--border-color);
  background-color: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
  z-index: 40;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 32px;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 12px;
}

.breadcrumb {
  font-size: 0.85rem;
  color: var(--text-subtle);
  display: flex;
  align-items: center;
  gap: 8px;
}

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

.breadcrumb a:hover {
  color: var(--accent-primary);
}

.breadcrumb span.current {
  color: var(--text-main);
  font-weight: 600;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

.badge-course {
  background-color: var(--accent-light);
  color: var(--accent-primary);
  border: 1px solid var(--accent-border);
  padding: 4px 10px;
  font-size: 0.75rem;
  font-weight: 600;
  border-radius: 9999px;
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

/* Content Container */
.content-container {
  max-width: var(--content-max-width);
  width: 100%;
  margin: 0 auto;
  padding: 36px 32px 80px;
  flex: 1;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  color: var(--text-main);
  line-height: 1.3;
}

h1 {
  font-size: 2.1rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: 8px;
}

.chapter-meta-tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent-primary);
  background: var(--accent-light);
  padding: 3px 10px;
  border-radius: 6px;
  margin-bottom: 12px;
  border: 1px solid var(--accent-border);
}

h2.section-heading {
  font-size: 1.45rem;
  font-weight: 700;
  letter-spacing: -0.01em;
  margin-top: 40px;
  margin-bottom: 20px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  gap: 10px;
}

p {
  font-size: 0.98rem;
  margin-bottom: 16px;
  color: var(--text-main);
}

.lead-text {
  font-size: 1.05rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin-bottom: 24px;
}

/* Inline Code */
:not(pre) > code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  color: var(--code-inline-text) !important;
  background-color: var(--code-inline-bg) !important;
  border: 1px solid var(--code-inline-border);
  padding: 2px 6px;
  border-radius: 5px;
  font-weight: 600;
}

/* Block Code */
.code-wrapper {
  position: relative;
  margin: 14px 0 20px;
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--code-border);
}

.code-header {
  background-color: var(--code-header-bg);
  padding: 6px 14px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--code-border);
}

.code-lang-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: #94a3b8;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-weight: 600;
}

.copy-code-btn {
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.2);
  color: #e2e8f0;
  padding: 3px 8px;
  font-size: 0.72rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 5px;
  transition: all var(--transition-fast);
}

.copy-code-btn:hover {
  background: rgba(255, 255, 255, 0.2);
  color: #ffffff;
}

.copy-code-btn.copied {
  background: #166534;
  border-color: #22c55e;
  color: #ffffff;
}

pre[class*="language-"] {
  margin: 0 !important;
  padding: 14px 16px !important;
  background: var(--code-block-bg) !important;
  font-family: var(--font-mono) !important;
  font-size: 0.88rem !important;
  line-height: 1.6 !important;
  border-radius: 0 !important;
  overflow-x: auto;
}

pre[class*="language-"] code {
  background: transparent !important;
  border: none !important;
  padding: 0 !important;
  color: #f1f5f9 !important;
  font-family: var(--font-mono) !important;
  font-size: 0.88rem !important;
  line-height: 1.6 !important;
  display: block !important;
  white-space: pre !important;
  box-shadow: none !important;
  border-radius: 0 !important;
}

/* Chapter Navigation Footer */
.chapter-nav-footer {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 60px;
  padding-top: 24px;
  border-top: 1px solid var(--border-color);
}

.chapter-nav-card {
  flex: 1;
  max-width: 48%;
  display: flex;
  flex-direction: column;
  padding: 16px 20px;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  text-decoration: none;
  background-color: var(--bg-card);
  transition: all var(--transition-fast);
}

.chapter-nav-card:hover {
  border-color: var(--accent-primary);
  transform: translateY(-2px);
  box-shadow: var(--shadow-sm);
}

.chapter-nav-card.next {
  text-align: right;
  margin-left: auto;
}

.chapter-nav-label {
  font-size: 0.72rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-subtle);
  margin-bottom: 4px;
}

.chapter-nav-title {
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--accent-primary);
}

@media (max-width: 900px) {
  .sidebar {
    transform: translateX(-100%);
  }

  .sidebar.open {
    transform: translateX(0);
    box-shadow: var(--shadow-lg);
  }

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

  .sidebar-toggle-btn {
    display: inline-block;
  }

  .top-header {
    padding: 0 16px;
  }

  .content-container {
    padding: 24px 16px 60px;
  }
}
/* Academic Tables */
.table-container {
  overflow-x: auto;
  margin: 16px 0 20px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
  background-color: var(--bg-card);
}

table.academic-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
  text-align: left;
}

table.academic-table th {
  background-color: var(--bg-secondary);
  color: var(--text-main);
  font-weight: 700;
  padding: 10px 16px;
  border-bottom: 2px solid var(--border-color);
}

table.academic-table td {
  padding: 10px 16px;
  border-bottom: 1px solid var(--border-color);
  color: var(--text-main);
}

table.academic-table tr:last-child td {
  border-bottom: none;
}

table.academic-table tr:hover td {
  background-color: var(--bg-tertiary);
}