/* ==========================================================================
   BRAIN KNOWLEDGE HUB — EDITORIAL ACADEMIC DESIGN SYSTEM
   Modern academic digital library aesthetic: off-white & warm cream,
   refined serif typography, high-contrast ink, and accessible dark mode.
   ========================================================================== */

:root {
  /* Color Palette - Light Editorial Paper */
  --bg-desk: #f5f2ea;
  --bg-paper: #fbf9f4;
  --bg-card: #ffffff;
  --bg-subtle: #ede7d8;
  --bg-hover: #e5ded0;
  
  --line-rule: #ded6c4;
  --line-strong: #c2b79e;
  
  --ink-primary: #181d26;
  --ink-secondary: #525a6c;
  --ink-muted: #788294;
  
  --accent-navy: #1a365d;
  --accent-navy-subtle: #e9f0fa;
  --accent-amber: #9a5800;
  --accent-amber-subtle: #fef3e0;
  --accent-forest: #1e6b42;
  --accent-forest-subtle: #e9f7ee;
  
  /* Typography */
  --font-serif: "Newsreader", "STIX Two Text", Georgia, "Times New Roman", serif;
  --font-sans: "Source Sans 3", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  --font-mono: "JetBrains Mono", Consolas, Menlo, Monaco, monospace;
  
  /* Layout & Shadows */
  --max-width: 1180px;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --shadow-sm: 0 1px 3px rgba(35, 25, 10, 0.06);
  --shadow-md: 0 4px 14px rgba(35, 25, 10, 0.08);
  --shadow-lg: 0 10px 28px rgba(35, 25, 10, 0.12);
  
  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;
}

html[data-theme="dark"] {
  /* Color Palette - Dark Library Study */
  --bg-desk: #0e121a;
  --bg-paper: #141924;
  --bg-card: #1a2130;
  --bg-subtle: #242c3d;
  --bg-hover: #2e384c;
  
  --line-rule: #2a3346;
  --line-strong: #3e4a63;
  
  --ink-primary: #f0f3f9;
  --ink-secondary: #a0abc0;
  --ink-muted: #6b778d;
  
  --accent-navy: #79b8ff;
  --accent-navy-subtle: #192a47;
  --accent-amber: #e6a13a;
  --accent-amber-subtle: #3a2a14;
  --accent-forest: #5cdb95;
  --accent-forest-subtle: #123321;
  
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.35);
  --shadow-md: 0 4px 14px rgba(0, 0, 0, 0.45);
  --shadow-lg: 0 10px 28px rgba(0, 0, 0, 0.55);
}

/* Base Reset & Box Sizing */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  background-color: var(--bg-desk);
  color: var(--ink-primary);
  font-family: var(--font-sans);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background-image: radial-gradient(var(--line-rule) 1px, transparent 1px);
  background-size: 28px 28px;
  background-position: 0 0;
}

a {
  color: var(--accent-navy);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  text-decoration: underline;
}

button {
  font-family: inherit;
  cursor: pointer;
}

/* Typography Helpers */
h1, h2, h3, h4 {
  font-family: var(--font-serif);
  font-weight: 600;
  line-height: 1.25;
  color: var(--ink-primary);
}

/* Header & Navigation Bar */
.hub-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: var(--bg-paper);
  border-bottom: 1px solid var(--line-rule);
  backdrop-filter: blur(8px);
  box-shadow: var(--shadow-sm);
}

.hub-header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0.85rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
}

.hub-brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  text-decoration: none;
  color: var(--ink-primary);
}

.hub-brand-logo {
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  background: var(--accent-navy);
  color: #ffffff;
  display: grid;
  place-items: center;
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 700;
}

.hub-brand-title {
  font-family: var(--font-serif);
  font-size: 1.35rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.hub-brand-badge {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  padding: 0.2rem 0.45rem;
  border-radius: var(--radius-sm);
  background-color: var(--bg-subtle);
  color: var(--ink-secondary);
}

.hub-nav-links {
  display: flex;
  align-items: center;
  gap: 1.25rem;
  list-style: none;
}

.hub-nav-links a {
  font-size: 0.95rem;
  font-weight: 500;
  color: var(--ink-secondary);
  padding: 0.35rem 0.5rem;
  border-radius: var(--radius-sm);
}

.hub-nav-links a:hover,
.hub-nav-links a.active {
  color: var(--accent-navy);
  text-decoration: none;
  background-color: var(--bg-subtle);
}

.hub-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

/* Quick Search Trigger Button */
.search-trigger-btn {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.45rem 0.85rem;
  background-color: var(--bg-card);
  border: 1px solid var(--line-rule);
  border-radius: var(--radius-md);
  color: var(--ink-muted);
  font-size: 0.88rem;
  transition: all var(--transition-fast);
}

.search-trigger-btn:hover {
  border-color: var(--line-strong);
  color: var(--ink-primary);
  box-shadow: var(--shadow-sm);
}

.search-trigger-btn kbd {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  background-color: var(--bg-subtle);
  color: var(--ink-secondary);
  padding: 0.15rem 0.35rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--line-rule);
}

/* Theme Toggle Button */
.theme-toggle-btn {
  background: transparent;
  border: 1px solid var(--line-rule);
  border-radius: var(--radius-md);
  width: 36px;
  height: 36px;
  display: grid;
  place-items: center;
  color: var(--ink-secondary);
  transition: all var(--transition-fast);
}

.theme-toggle-btn:hover {
  background-color: var(--bg-subtle);
  color: var(--ink-primary);
}

/* Main Container */
.hub-main {
  flex: 1;
  max-width: var(--max-width);
  width: 100%;
  margin: 0 auto;
  padding: 2.5rem 1.5rem 4rem;
}

/* Hero Section */
.hero-section {
  text-align: center;
  max-width: 800px;
  margin: 1.5rem auto 3.5rem;
}

.hero-tagline {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--accent-amber);
  background-color: var(--accent-amber-subtle);
  padding: 0.3rem 0.75rem;
  border-radius: 20px;
  margin-bottom: 1.25rem;
  border: 1px solid rgba(184, 110, 0, 0.2);
}

.hero-title {
  font-size: 2.85rem;
  letter-spacing: -0.02em;
  margin-bottom: 1rem;
  color: var(--ink-primary);
}

.hero-subtitle {
  font-size: 1.15rem;
  color: var(--ink-secondary);
  line-height: 1.6;
  margin-bottom: 2rem;
}

/* In-Hero Search Input */
.hero-search-wrapper {
  position: relative;
  max-width: 620px;
  margin: 0 auto 2.5rem;
}

.hero-search-input {
  width: 100%;
  padding: 0.95rem 1.2rem 0.95rem 3.1rem;
  font-size: 1.05rem;
  font-family: var(--font-sans);
  background-color: var(--bg-card);
  color: var(--ink-primary);
  border: 2px solid var(--line-rule);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  transition: all var(--transition-fast);
  outline: none;
}

.hero-search-input:focus {
  border-color: var(--accent-navy);
  box-shadow: 0 0 0 4px var(--accent-navy-subtle), var(--shadow-md);
}

.hero-search-icon {
  position: absolute;
  left: 1.1rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--ink-muted);
  pointer-events: none;
  display: flex;
}

/* Stats Ribbon */
.stats-ribbon {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 2.5rem;
  margin: 1.5rem auto 0;
  padding-top: 1.5rem;
  border-top: 1px dashed var(--line-rule);
}

.stat-item {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.stat-value {
  font-family: var(--font-serif);
  font-size: 1.65rem;
  font-weight: 700;
  color: var(--accent-navy);
  line-height: 1.2;
}

.stat-label {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--ink-muted);
}

/* Section Common Headers */
.section-header {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  margin-bottom: 1.5rem;
  padding-bottom: 0.75rem;
  border-bottom: 2px solid var(--line-rule);
}

.section-title {
  font-size: 1.75rem;
  letter-spacing: -0.01em;
}

.section-subtitle {
  font-size: 0.9rem;
  color: var(--ink-muted);
}

/* Featured Section */
.featured-section {
  margin-bottom: 4rem;
}

.featured-card {
  background: var(--bg-card);
  border: 1px solid var(--line-rule);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-md);
  position: relative;
  overflow: hidden;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 2rem;
  align-items: center;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.featured-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
  border-color: var(--line-strong);
}

.featured-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 6px;
  height: 100%;
  background-color: var(--accent-amber);
}

.featured-meta {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.75rem;
  flex-wrap: wrap;
}

.badge {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 600;
  padding: 0.2rem 0.55rem;
  border-radius: var(--radius-sm);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.badge-subject {
  background-color: var(--accent-navy-subtle);
  color: var(--accent-navy);
}

.badge-category {
  background-color: var(--bg-subtle);
  color: var(--ink-secondary);
}

.badge-featured {
  background-color: var(--accent-amber-subtle);
  color: var(--accent-amber);
  border: 1px solid rgba(184, 110, 0, 0.3);
}

.featured-title {
  font-size: 1.85rem;
  margin-bottom: 0.65rem;
}

.featured-title a {
  color: var(--ink-primary);
}

.featured-title a:hover {
  color: var(--accent-navy);
}

.featured-desc {
  color: var(--ink-secondary);
  font-size: 1.05rem;
  line-height: 1.6;
  margin-bottom: 1.25rem;
  max-width: 750px;
}

.featured-tags {
  display: flex;
  gap: 0.45rem;
  flex-wrap: wrap;
  align-items: center;
}

.tag-pill {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--ink-muted);
  background-color: var(--bg-subtle);
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
}

.featured-action {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 0.75rem;
  min-width: 180px;
}

.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.4rem;
  background-color: var(--accent-navy);
  color: #ffffff !important;
  font-weight: 600;
  font-size: 0.95rem;
  border-radius: var(--radius-md);
  border: none;
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.btn-primary:hover {
  background-color: #122847;
  text-decoration: none;
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
}

.notebook-stats-pill {
  font-size: 0.8rem;
  color: var(--ink-muted);
  text-align: right;
}

/* Subjects Grid */
.subjects-section {
  margin-bottom: 4rem;
}

.subjects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1.5rem;
}

.subject-card {
  background-color: var(--bg-card);
  border: 1px solid var(--line-rule);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-fast);
  position: relative;
  text-decoration: none !important;
}

.subject-card:hover {
  transform: translateY(-2px);
  border-color: var(--line-strong);
  box-shadow: var(--shadow-md);
}

.subject-card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.75rem;
}

.subject-name {
  font-size: 1.35rem;
  color: var(--ink-primary);
  transition: color var(--transition-fast);
}

.subject-card:hover .subject-name {
  color: var(--accent-navy);
}

.subject-count-badge {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 600;
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
}

.subject-count-active {
  background-color: var(--accent-forest-subtle);
  color: var(--accent-forest);
  border: 1px solid rgba(30, 107, 66, 0.2);
}

.subject-count-incubation {
  background-color: var(--bg-subtle);
  color: var(--ink-muted);
}

.subject-card-desc {
  font-size: 0.92rem;
  color: var(--ink-secondary);
  line-height: 1.5;
  margin-bottom: 1.25rem;
  flex: 1;
}

.subject-card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 0.85rem;
  border-top: 1px solid var(--line-rule);
  font-size: 0.85rem;
  color: var(--ink-muted);
}

.subject-card-arrow {
  color: var(--accent-navy);
  font-weight: 700;
  transition: transform var(--transition-fast);
}

.subject-card:hover .subject-card-arrow {
  transform: translateX(4px);
}

/* Subject Catalog Page Layout */
.subject-page-hero {
  margin-bottom: 2.5rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px solid var(--line-rule);
}

.breadcrumbs {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.88rem;
  color: var(--ink-muted);
  margin-bottom: 0.75rem;
}

.breadcrumbs a {
  color: var(--ink-secondary);
}

.breadcrumbs a:hover {
  color: var(--accent-navy);
}

.subject-page-title {
  font-size: 2.5rem;
  margin-bottom: 0.5rem;
}

.subject-page-desc {
  font-size: 1.1rem;
  color: var(--ink-secondary);
  max-width: 800px;
}

/* Notebook Cards List (Subject View) */
.notebooks-list {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.notebook-card {
  background-color: var(--bg-card);
  border: 1px solid var(--line-rule);
  border-radius: var(--radius-md);
  padding: 1.75rem;
  box-shadow: var(--shadow-sm);
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 1.5rem;
  align-items: center;
  transition: all var(--transition-fast);
}

.notebook-card:hover {
  border-color: var(--line-strong);
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
}

.notebook-card-content {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.notebook-card-title {
  font-size: 1.45rem;
}

.notebook-card-title a {
  color: var(--ink-primary);
}

.notebook-card-title a:hover {
  color: var(--accent-navy);
}

.notebook-card-desc {
  font-size: 0.95rem;
  color: var(--ink-secondary);
  line-height: 1.55;
}

/* Empty State Component */
.empty-state {
  text-align: center;
  background-color: var(--bg-card);
  border: 1px dashed var(--line-strong);
  border-radius: var(--radius-lg);
  padding: 4rem 2rem;
  margin: 2rem 0;
}

.empty-state-icon {
  font-size: 2.5rem;
  margin-bottom: 1rem;
  color: var(--ink-muted);
}

.empty-state-title {
  font-size: 1.6rem;
  margin-bottom: 0.6rem;
}

.empty-state-desc {
  font-size: 1rem;
  color: var(--ink-secondary);
  max-width: 540px;
  margin: 0 auto 1.75rem;
  line-height: 1.6;
}

/* Search Modal Overlay */
.search-modal-backdrop {
  position: fixed;
  inset: 0;
  background-color: rgba(14, 18, 26, 0.65);
  backdrop-filter: blur(4px);
  z-index: 1000;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding: 12vh 1rem 2rem;
}

.search-modal-backdrop.active {
  display: flex;
}

.search-modal {
  background-color: var(--bg-card);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  width: 100%;
  max-width: 640px;
  overflow: hidden;
  animation: modalSlide 0.18s ease-out;
}

@keyframes modalSlide {
  from { opacity: 0; transform: translateY(-12px); }
  to { opacity: 1; transform: translateY(0); }
}

.search-modal-header {
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--line-rule);
  display: flex;
  align-items: center;
  gap: 0.75rem;
  background-color: var(--bg-paper);
}

.search-modal-input {
  flex: 1;
  background: transparent;
  border: none;
  font-size: 1.15rem;
  font-family: var(--font-sans);
  color: var(--ink-primary);
  outline: none;
}

.search-modal-close {
  background: transparent;
  border: none;
  font-size: 1.2rem;
  color: var(--ink-muted);
  padding: 0.25rem;
  cursor: pointer;
}

.search-modal-results {
  max-height: 420px;
  overflow-y: auto;
  padding: 0.5rem;
}

.search-result-item {
  display: block;
  padding: 0.85rem 1rem;
  border-radius: var(--radius-md);
  color: var(--ink-primary);
  text-decoration: none !important;
  transition: background var(--transition-fast);
}

.search-result-item:hover,
.search-result-item.selected {
  background-color: var(--bg-subtle);
}

.search-result-title {
  font-family: var(--font-serif);
  font-size: 1.15rem;
  font-weight: 600;
  margin-bottom: 0.25rem;
  color: var(--accent-navy);
}

.search-result-snippet {
  font-size: 0.85rem;
  color: var(--ink-secondary);
  line-height: 1.45;
}

.search-result-snippet mark {
  background-color: rgba(230, 161, 58, 0.35);
  color: inherit;
  font-weight: 600;
  border-radius: 2px;
  padding: 0 2px;
}

.search-result-meta {
  display: flex;
  gap: 0.5rem;
  margin-top: 0.4rem;
  font-size: 0.75rem;
  color: var(--ink-muted);
  font-family: var(--font-mono);
}

.search-modal-footer {
  padding: 0.65rem 1.25rem;
  border-top: 1px solid var(--line-rule);
  background-color: var(--bg-paper);
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 0.75rem;
  color: var(--ink-muted);
}

.search-modal-footer kbd {
  font-family: var(--font-mono);
  background-color: var(--bg-subtle);
  border: 1px solid var(--line-rule);
  padding: 0.15rem 0.35rem;
  border-radius: var(--radius-sm);
  color: var(--ink-secondary);
}

/* Portal Return Bar (Injected into published notebooks) */
.hub-portal-bar {
  background-color: var(--bg-paper, #fcf8ee);
  border-bottom: 1px solid var(--line-rule, #d6e3ef);
  padding: 0.45rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-family: var(--font-sans, system-ui, sans-serif);
  font-size: 0.85rem;
  color: var(--ink-secondary, #5a5d66);
  z-index: 9999;
  position: relative;
}

.hub-portal-bar a {
  color: var(--accent-navy, #1d3c8c);
  font-weight: 600;
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.hub-portal-bar a:hover {
  text-decoration: underline;
}

.hub-portal-bar-crumbs {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

/* Footer */
.hub-footer {
  border-top: 1px solid var(--line-rule);
  background-color: var(--bg-paper);
  padding: 2.5rem 1.5rem;
  margin-top: auto;
}

.hub-footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
  flex-wrap: wrap;
  font-size: 0.88rem;
  color: var(--ink-muted);
}

.hub-footer-links {
  display: flex;
  align-items: center;
  gap: 1.5rem;
}

.hub-footer-links a {
  color: var(--ink-secondary);
}

.hub-footer-links a:hover {
  color: var(--accent-navy);
}

/* Responsive Media Queries */
@media (max-width: 860px) {
  .hero-title {
    font-size: 2.2rem;
  }
  .featured-card {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }
  .featured-action {
    align-items: flex-start;
  }
  .hub-nav-links {
    display: none;
  }
}

@media (max-width: 580px) {
  .hero-title {
    font-size: 1.85rem;
  }
  .stats-ribbon {
    flex-wrap: wrap;
    gap: 1.25rem;
  }
  .notebook-card {
    grid-template-columns: 1fr;
  }
}