:root {
  --bg-primary: #f8fafc;
  --bg-surface: #ffffff;
  --bg-card: #ffffff;
  --bg-subtle: #f1f5f9;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --border-color: #e2e8f0;
  --border-subtle: #cbd5e1;
  --primary-accent: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eff6ff;
  --accent-gradient: linear-gradient(135deg, #2563eb 0%, #4f46e5 100%);
  --sidebar-width: 320px;
  --header-height: 64px;
  --math-bg: #f8fafc;
  --math-filter: none;
  --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);
}

[data-theme="dark"] {
  --bg-primary: #0b0f19;
  --bg-surface: #111827;
  --bg-card: #151d2e;
  --bg-subtle: #1e293b;
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --border-color: #1e293b;
  --border-subtle: #334155;
  --primary-accent: #3b82f6;
  --primary-hover: #60a5fa;
  --primary-light: rgba(59, 130, 246, 0.15);
  --accent-gradient: linear-gradient(135deg, #3b82f6 0%, #6366f1 100%);
  --math-bg: #131b2c;
  --math-filter: invert(0.92) hue-rotate(180deg) brightness(1.1);
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.5);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.4);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.4);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 80px;
}

body {
  margin: 0;
  padding: 0;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family:
    -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
    Arial, sans-serif;
  font-size: 16px;
  line-height: 1.75;
  transition:
    background-color 0.3s ease,
    color 0.3s ease;
  overflow-x: hidden;
}

/* Reading progress bar */
#reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  width: 0%;
  background: var(--accent-gradient);
  z-index: 10000;
  transition: width 0.1s ease;
}

/* Modern Sticky Navigation Bar */
.modern-navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px;
  z-index: 9999;
  transition:
    background-color 0.3s ease,
    border-color 0.3s ease;
}

[data-theme="dark"] .modern-navbar {
  background: rgba(17, 24, 39, 0.85);
}

.nav-brand-group {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 15px;
}

.brand-link {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-primary);
  text-decoration: none;
  font-weight: 700;
  letter-spacing: -0.01em;
  transition: color 0.2s;
}

.brand-link:hover {
  color: var(--primary-accent);
}

.brand-logo-icon {
  width: 28px;
  height: 28px;
  border-radius: 8px;
  background: var(--accent-gradient);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #ffffff;
  font-weight: 800;
  font-size: 14px;
  box-shadow: 0 2px 4px rgba(37, 99, 235, 0.3);
}

.breadcrumb-sep {
  color: var(--text-muted);
  font-size: 13px;
}

.breadcrumb-text {
  color: var(--text-secondary);
  font-weight: 500;
  max-width: 260px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 10px;
}

.nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 14px;
  font-size: 14px;
  font-weight: 600;
  border-radius: 8px;
  cursor: pointer;
  border: 1px solid var(--border-color);
  background: var(--bg-surface);
  color: var(--text-primary);
  text-decoration: none;
  transition: all 0.2s ease;
  user-select: none;
}

.nav-btn:hover {
  background: var(--bg-subtle);
  border-color: var(--border-subtle);
  color: var(--primary-accent);
}

.nav-btn.primary-btn {
  background: var(--accent-gradient);
  color: #ffffff;
  border: none;
  box-shadow: 0 2px 6px rgba(37, 99, 235, 0.25);
}

.nav-btn.primary-btn:hover {
  opacity: 0.95;
  transform: translateY(-1px);
  box-shadow: 0 4px 10px rgba(37, 99, 235, 0.35);
}

.nav-btn.icon-only {
  padding: 8px;
  border-radius: 8px;
}

/* Master Layout Container */
.master-layout {
  display: flex;
  margin-top: var(--header-height);
  min-height: calc(100vh - var(--header-height));
  position: relative;
  width: 100%;
  max-width: 100vw;
  overflow-x: hidden;
}

/* Sticky Left Sidebar (Table of Contents) */
.toc-sidebar {
  width: var(--sidebar-width);
  flex-shrink: 0;
  height: calc(100vh - var(--header-height));
  position: sticky;
  top: var(--header-height);
  background: var(--bg-surface);
  border-right: 1px solid var(--border-color);
  overflow-y: auto;
  padding: 24px 16px;
  transition:
    transform 0.3s cubic-bezier(0.4, 0, 0.2, 1),
    background-color 0.3s ease;
}

.toc-sidebar::-webkit-scrollbar {
  width: 6px;
}

.toc-sidebar::-webkit-scrollbar-thumb {
  background-color: var(--border-subtle);
  border-radius: 3px;
}

.toc-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-bottom: 12px;
  margin-bottom: 16px;
  border-bottom: 1px solid var(--border-color);
}

.toc-title {
  font-size: 14px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
}

.toc-filter {
  width: 100%;
  padding: 8px 12px;
  font-size: 13px;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background: var(--bg-subtle);
  color: var(--text-primary);
  margin-bottom: 16px;
  outline: none;
  transition: border-color 0.2s;
}

.toc-filter:focus {
  border-color: var(--primary-accent);
}

/* TOC Items Styling */
.tableofcontents {
  font-size: 13.5px;
  line-height: 1.35;
}

.tableofcontents br {
  display: none !important;
}

.tableofcontents a {
  color: var(--text-secondary);
  text-decoration: none;
  transition: color 0.15s ease;
  display: inline;
}

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

.tableofcontents .sectionToc {
  font-weight: 700;
  color: var(--text-primary);
  margin-top: 10px;
  margin-bottom: 2px;
  padding: 3px 6px;
  border-radius: 6px;
  display: block;
  line-height: 1.35;
  transition:
    background-color 0.15s ease,
    color 0.15s ease;
}

.tableofcontents .sectionToc:hover {
  background-color: var(--bg-subtle);
  color: var(--primary-accent);
}

.tableofcontents .subsectionToc {
  margin-left: 12px;
  margin-top: 2px;
  margin-bottom: 2px;
  padding: 2px 6px;
  border-radius: 6px;
  color: var(--text-secondary);
  display: block;
  line-height: 1.35;
  transition:
    background-color 0.15s ease,
    color 0.15s ease;
}

.tableofcontents .subsectionToc:hover {
  background-color: var(--bg-subtle);
  color: var(--primary-accent);
}

.tableofcontents .subsubsectionToc {
  margin-left: 24px;
  margin-top: 1px;
  margin-bottom: 1px;
  padding: 2px 6px;
  border-radius: 6px;
  color: var(--text-muted);
  display: block;
  font-size: 12.5px;
  line-height: 1.35;
  transition:
    background-color 0.15s ease,
    color 0.15s ease;
}

.tableofcontents .subsubsectionToc:hover {
  background-color: var(--bg-subtle);
  color: var(--primary-accent);
}

/* Main Reader Content Area */
.main-reader-content {
  flex: 1 1 auto;
  min-width: 0;
  width: 100%;
  max-width: 1000px;
  margin: 0 auto;
  padding: 40px 48px 120px 48px;
  box-sizing: border-box;
  overflow-x: hidden;
}

/* Hero Section */
.reader-hero {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 16px;
  padding: 36px 40px;
  margin-bottom: 40px;
  box-shadow: var(--shadow-sm);
  position: relative;
  overflow: hidden;
}

.reader-hero::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--accent-gradient);
}

.reader-hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--primary-light);
  color: var(--primary-accent);
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 13px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 16px;
}

.reader-hero-title {
  font-size: 32px;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  margin: 0 0 12px 0;
  line-height: 1.25;
}

.reader-hero-desc {
  font-size: 16px;
  color: var(--text-secondary);
  margin: 0 0 20px 0;
  line-height: 1.6;
}

.reader-hero-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 20px;
  font-size: 14px;
  color: var(--text-muted);
  border-top: 1px solid var(--border-color);
  padding-top: 18px;
}

.reader-hero-meta-item {
  display: flex;
  align-items: center;
  gap: 6px;
}

/* Typography & Headings */
h2,
h3,
h4,
h5,
h6 {
  color: var(--text-primary);
  font-weight: 700;
  letter-spacing: -0.015em;
  margin-top: 2.2em;
  margin-bottom: 0.8em;
  line-height: 1.35;
}

.sectionHead {
  font-size: 24px;
  border-bottom: 2px solid var(--border-color);
  padding-bottom: 8px;
  margin-top: 50px;
  color: var(--primary-accent);
}

.subsectionHead {
  font-size: 20px;
  color: var(--text-primary);
  margin-top: 36px;
}

.subsubsectionHead {
  font-size: 17px;
  color: var(--text-secondary);
  margin-top: 28px;
}

p {
  margin-top: 0;
  margin-bottom: 1.2em;
  color: var(--text-primary);
}

a {
  color: var(--primary-accent);
  text-decoration: none;
  transition: color 0.2s;
}

a:hover {
  text-decoration: underline;
}

/* Math Display Containers */
div.math-display,
div.par-math-display {
  text-align: center;
  background: var(--math-bg);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 16px 20px;
  margin: 24px 0;
  overflow-x: auto;
  box-shadow: var(--shadow-sm);
  transition:
    background-color 0.3s ease,
    border-color 0.3s ease;
}

table.equation,
table.eqnarray,
table.eqnarray-star {
  width: 100%;
  background: var(--math-bg);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 12px 16px;
  margin: 24px 0;
  overflow-x: auto;
}

/* Ensure all content images and diagrams fit cleanly within site width */
.main-reader-content img {
  max-width: 100% !important;
  height: auto !important;
  box-sizing: border-box;
}

.main-reader-content figure.figure,
.main-reader-content div.figure,
.main-reader-content figure.float,
.main-reader-content div.float {
  max-width: 100% !important;
  width: 100% !important;
  margin: 2.5rem auto !important;
  text-align: center;
  box-sizing: border-box;
  overflow: hidden;
  clear: both;
}

.main-reader-content figure.figure img,
.main-reader-content div.figure img,
.main-reader-content figure.float img,
.main-reader-content div.float img,
.main-reader-content img[alt="PIC"],
.main-reader-content img.graphics {
  max-width: 100% !important;
  width: auto !important;
  height: auto !important;
  display: block;
  margin: 1.5rem auto !important;
  border-radius: 8px;
  box-shadow: var(--shadow-sm);
  background-color: var(--bg-surface);
  box-sizing: border-box;
}

/* Captions below figures */
figcaption.caption,
div.caption {
  font-size: 14px;
  color: var(--text-secondary);
  margin-top: 12px;
  margin-left: auto !important;
  margin-right: auto !important;
  text-align: center !important;
  text-indent: 0 !important;
  line-height: 1.5;
  max-width: 90%;
}

figcaption.caption span.id,
div.caption span.id {
  font-weight: 700;
  color: var(--text-primary);
}

/* Math Image Inversion in Dark Mode - invert math symbols only */
img.math,
img.math-display,
.math-display img {
  vertical-align: middle;
  filter: var(--math-filter);
  transition: filter 0.3s ease;
}

/* Do not invert photos, diagrams, and figures in dark mode */
img[alt="PIC"],
img.graphics,
figure img,
div.figure img,
img[src*="images/"],
img[src*="data/"] {
  filter: none !important;
}

/* Verbatim / Code Blocks */
pre.verbatim {
  background: #0f172a;
  color: #e2e8f0;
  padding: 18px 22px;
  border-radius: 10px;
  font-family:
    "SFMono-Regular", Consolas, "Liberation Mono", Menlo, Courier, monospace;
  font-size: 14px;
  line-height: 1.6;
  overflow-x: auto;
  box-shadow: var(--shadow-md);
  margin: 24px 0;
}

/* Tables */
table.tabular {
  width: 100%;
  border-collapse: separate;
  border-spacing: 0;
  margin: 24px 0;
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}

table.tabular td,
table.tabular th {
  padding: 12px 16px;
  border-bottom: 1px solid var(--border-color);
  font-size: 14.5px;
}

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

table.tabular tr:nth-child(even) {
  background-color: var(--bg-subtle);
}

/* Floating Action Button (Back to Top) */
.back-to-top-btn {
  position: fixed;
  bottom: 28px;
  right: 28px;
  width: 46px;
  height: 46px;
  border-radius: 50%;
  background: var(--accent-gradient);
  color: #ffffff;
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  z-index: 9998;
}

.back-to-top-btn.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 12px 20px -3px rgba(37, 99, 235, 0.4);
}

/* Mobile Responsiveness */
@media (max-width: 960px) {
  .master-layout {
    display: block;
    width: 100%;
    max-width: 100vw;
    overflow-x: hidden;
  }

  .toc-sidebar {
    position: fixed;
    top: var(--header-height);
    left: 0;
    bottom: 0;
    width: min(320px, 85vw);
    z-index: 9990;
    transform: translateX(-100%);
    box-shadow: var(--shadow-lg);
  }

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

  .main-reader-content {
    width: 100% !important;
    max-width: 100% !important;
    min-width: 0 !important;
    padding: 20px 16px 80px 16px !important;
    box-sizing: border-box !important;
  }

  .main-reader-content figure.figure,
  .main-reader-content div.figure,
  .main-reader-content figure.float,
  .main-reader-content div.float {
    margin: 1.5rem auto !important;
    width: 100% !important;
    max-width: 100% !important;
  }

  .main-reader-content figure.figure img,
  .main-reader-content div.figure img,
  .main-reader-content figure.float img,
  .main-reader-content div.float img,
  .main-reader-content img[alt="PIC"],
  .main-reader-content img.graphics {
    max-width: 100% !important;
    width: 100% !important;
    height: auto !important;
    object-fit: contain;
  }

  .reader-hero {
    padding: 24px 16px;
  }

  .reader-hero-title {
    font-size: 24px;
  }

  .breadcrumb-text {
    display: none;
  }
}