/* Quantum Mechanics Standard Textbook Edition Stylesheet */
:root {
  --bg-dark: #0a0e17;
  --bg-card: #111827;
  --bg-card-hover: #1e293b;
  --border-color: #1f293d;
  --accent-cyan: #38bdf8;
  --accent-emerald: #10b981;
  --accent-amber: #f59e0b;
  --accent-rose: #f43f5e;
  --text-main: #f1f5f9;
  --text-muted: #94a3b8;
  --text-body: #e2e8f0;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  --font-serif: 'Newsreader', Georgia, Cambria, serif;
  --font-mono: 'Fira Code', monospace;
}

body.academic-font {
  --font-body: var(--font-serif);
}

body:not(.academic-font) {
  --font-body: var(--font-sans);
}

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

body {
  background-color: var(--bg-dark);
  color: var(--text-main);
  font-family: var(--font-sans);
  line-height: 1.75;
  overflow-x: hidden;
  user-select: none; /* Anti-copy protective measure */
  -webkit-user-select: none;
}

/* App Layout Grid */
.app-container {
  display: flex;
  min-height: 100vh;
}

/* Left Navigation Sidebar */
.sidebar {
  width: 310px;
  background-color: #0d1322;
  border-right: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  position: sticky;
  top: 0;
  height: 100vh;
  z-index: 40;
}

.brand-header {
  padding: 1.25rem 1.5rem;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.brand-logo-img {
  width: 36px;
  height: 36px;
  border-radius: 9px;
  box-shadow: 0 4px 12px rgba(56, 189, 248, 0.25);
  display: block;
}

.brand-title {
  font-weight: 700;
  font-size: 1.05rem;
  color: #fff;
  letter-spacing: -0.02em;
}

.brand-subtitle {
  font-size: 0.73rem;
  color: var(--accent-cyan);
  font-weight: 500;
}

/* Search Bar in Sidebar */
.search-box-container {
  padding: 0.75rem 1.25rem 0.5rem;
}

.search-input {
  width: 100%;
  background-color: #111827;
  border: 1px solid #1f293d;
  color: #fff;
  padding: 0.55rem 0.85rem;
  border-radius: 6px;
  font-size: 0.8rem;
  outline: none;
  transition: border-color 0.2s;
}

.search-input:focus {
  border-color: var(--accent-cyan);
}

.nav-section-title {
  padding: 0.75rem 1.5rem 0.4rem;
  font-size: 0.7rem;
  text-transform: uppercase;
  color: var(--text-muted);
  font-weight: 700;
  letter-spacing: 0.05em;
}

.unit-nav-list {
  list-style: none;
  overflow-y: auto;
  flex: 1;
  padding: 0 0.75rem;
}

.unit-nav-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 0.9rem;
  margin-bottom: 0.35rem;
  border-radius: 8px;
  cursor: pointer;
  color: var(--text-muted);
  font-size: 0.86rem;
  font-weight: 500;
  transition: all 0.2s ease;
  border: 1px solid transparent;
}

.unit-nav-item:hover {
  background-color: #1e293b;
  color: #fff;
}

.unit-nav-item.active {
  background: linear-gradient(135deg, rgba(56, 189, 248, 0.15), rgba(59, 130, 246, 0.1));
  border-color: rgba(56, 189, 248, 0.4);
  color: #fff;
}

.unit-nav-num {
  font-size: 0.75rem;
  font-weight: 700;
  background-color: #1e293b;
  padding: 0.2rem 0.5rem;
  border-radius: 4px;
  color: var(--accent-cyan);
}

.unit-nav-item.active .unit-nav-num {
  background-color: var(--accent-cyan);
  color: #0b0f19;
}

/* Timer Badge in Sidebar */
.study-tracker-box {
  padding: 1.25rem;
  background: #090e1a;
  border-top: 1px solid var(--border-color);
}

.study-timer-display {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.5rem;
}

.timer-label {
  font-size: 0.75rem;
  color: var(--text-muted);
}

.timer-digits {
  font-family: var(--font-mono);
  font-weight: 700;
  color: var(--accent-emerald);
  font-size: 1.05rem;
}

.ad-progress-bar-bg {
  height: 6px;
  background-color: #1e293b;
  border-radius: 999px;
  overflow: hidden;
  margin-bottom: 0.6rem;
}

.ad-progress-bar-fill {
  height: 100%;
  width: 15%;
  background: linear-gradient(90deg, var(--accent-cyan), var(--accent-emerald));
  transition: width 1s linear;
}

.btn-preview-ad {
  width: 100%;
  padding: 0.45rem;
  font-size: 0.72rem;
  border-radius: 6px;
  background-color: #1e293b;
  color: #cbd5e1;
  border: 1px solid #334155;
  cursor: pointer;
  transition: background 0.2s;
}

.btn-preview-ad:hover {
  background-color: #334155;
  color: #fff;
}

/* Main Content Area */
.main-wrapper {
  flex: 1;
  display: flex;
  flex-direction: column;
  min-width: 0;
}

/* Top Sticky Bar */
.top-navbar {
  height: 64px;
  background: rgba(13, 19, 34, 0.85);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 2rem;
  position: sticky;
  top: 0;
  z-index: 30;
}

.course-badge-container {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.badge-pill {
  font-size: 0.75rem;
  padding: 0.25rem 0.6rem;
  border-radius: 999px;
  font-weight: 600;
}

.badge-course {
  background-color: rgba(56, 189, 248, 0.15);
  color: var(--accent-cyan);
  border: 1px solid rgba(56, 189, 248, 0.3);
}

.badge-credits {
  background-color: rgba(16, 185, 129, 0.15);
  color: var(--accent-emerald);
}

.navbar-actions {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.btn-tool {
  padding: 0.35rem 0.75rem;
  font-size: 0.75rem;
  font-weight: 600;
  border-radius: 6px;
  background-color: #1e293b;
  color: var(--accent-cyan);
  border: 1px solid #334155;
  cursor: pointer;
}

.protection-notice {
  font-size: 0.78rem;
  color: #cbd5e1;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

/* Content Columns Layout (Full-Width Focused Reader) */
.content-columns {
  display: flex;
  flex: 1;
  padding: 2.5rem 3.5rem;
  max-width: 1180px;
  margin: 0 auto;
  width: 100%;
  justify-content: center;
}

.reader-main-column {
  width: 100%;
  max-width: 100%;
  min-width: 0;
  font-family: var(--font-body);
}

.ads-sidebar-column {
  display: none;
}

/* Chapter Hero */
.unit-hero {
  background: linear-gradient(135deg, #111827, #0f172a);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: 2.5rem;
  margin-bottom: 2.5rem;
}

.unit-number-tag {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--accent-cyan);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.5rem;
}

.unit-title-heading {
  font-size: 2.2rem;
  font-weight: 800;
  color: #fff;
  letter-spacing: -0.02em;
  margin-bottom: 1rem;
  line-height: 1.25;
}

.unit-desc-lead {
  font-size: 1.05rem;
  color: var(--text-muted);
  line-height: 1.7;
}

/* Textbook Sections */
.textbook-section-card {
  background-color: #0e1424;
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: 2.25rem 2.5rem;
  margin-bottom: 2.5rem;
}

.sec-header {
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 1rem;
  margin-bottom: 1.5rem;
}

.sec-title {
  font-size: 1.45rem;
  font-weight: 700;
  color: #fff;
  display: flex;
  align-items: baseline;
  gap: 0.75rem;
}

.sec-num {
  color: var(--accent-cyan);
  font-family: var(--font-mono);
  font-size: 1.2rem;
}

.sec-content {
  font-size: 1.02rem;
  color: var(--text-body);
  line-height: 1.85;
}

.sec-content h4 {
  color: #38bdf8;
  font-size: 1.15rem;
  margin: 1.75rem 0 0.75rem;
  font-weight: 700;
  border-left: 3px solid #38bdf8;
  padding-left: 0.75rem;
}

.sec-content p {
  margin-bottom: 1.25rem;
}

.sec-content ul, .sec-content ol {
  margin: 1rem 0 1.25rem 1.75rem;
}

.sec-content li {
  margin-bottom: 0.5rem;
}

.sec-content strong {
  color: #fff;
}

.math-display {
  margin: 1.5rem 0;
  overflow-x: auto;
  overflow-y: hidden;
  text-align: center;
  padding: 0.5rem 0;
}

/* Simulation Section Cards */
.textbook-simulations-section {
  margin: 3.5rem 0;
}

.section-title-wrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin: 2rem 0 1.25rem;
}

.section-title {
  font-size: 1.35rem;
  font-weight: 700;
  color: #fff;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.simulation-slot {
  margin: 2rem 0;
  background-color: #0e1526;
  border: 1px solid #1e293b;
  border-radius: 12px;
  overflow: hidden;
  box-shadow: 0 10px 30px -5px rgba(0, 0, 0, 0.5);
}

.sim-wrapper {
  padding: 1.5rem;
}

.sim-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
  margin-bottom: 1.25rem;
}

.sim-badge {
  font-size: 0.72rem;
  font-weight: 700;
  background-color: rgba(56, 189, 248, 0.2);
  color: var(--accent-cyan);
  padding: 0.25rem 0.55rem;
  border-radius: 4px;
  margin-right: 0.5rem;
}

.sim-title {
  font-size: 1rem;
  color: #fff;
}

.sim-controls {
  display: flex;
  gap: 0.5rem;
}

.btn-control {
  padding: 0.45rem 0.9rem;
  border-radius: 6px;
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  background-color: #1e293b;
  color: #e2e8f0;
  border: 1px solid #334155;
  transition: all 0.2s;
}

.btn-control:hover {
  background-color: #334155;
}

.btn-control.active {
  background-color: var(--accent-cyan);
  color: #0b0f19;
  border-color: var(--accent-cyan);
}

.btn-control.active-danger {
  background-color: var(--accent-rose);
  color: #fff;
  border-color: var(--accent-rose);
}

.btn-n, .btn-sho, .btn-orb {
  padding: 0.35rem 0.75rem;
  border-radius: 6px;
  font-size: 0.78rem;
  font-weight: 600;
  cursor: pointer;
  background-color: #1e293b;
  color: #94a3b8;
  border: 1px solid #334155;
}

.btn-n.active, .btn-sho.active, .btn-orb.active {
  background-color: var(--accent-cyan);
  color: #090e17;
  border-color: var(--accent-cyan);
}

.canvas-container {
  position: relative;
  border-radius: 8px;
  overflow: hidden;
  border: 1px solid #1f293d;
  background-color: #000;
}

.canvas-container canvas {
  width: 100%;
  height: auto;
  display: block;
}

.sim-watermark {
  position: absolute;
  bottom: 8px;
  right: 12px;
  font-size: 0.68rem;
  color: rgba(255, 255, 255, 0.2);
  pointer-events: none;
  font-family: var(--font-mono);
}

.slider-control-group {
  margin-top: 0.75rem;
}

.slider-control-group label {
  display: block;
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: 0.3rem;
}

.range-slider {
  width: 100%;
  height: 6px;
  background: #1e293b;
  border-radius: 5px;
  outline: none;
  cursor: pointer;
  accent-color: var(--accent-cyan);
}

.sim-metrics-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 0.75rem;
  margin-top: 1rem;
}

.metric-card {
  background-color: #11192b;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 0.75rem 1rem;
}

.metric-card.highlight {
  border-color: rgba(16, 185, 129, 0.4);
  background-color: rgba(16, 185, 129, 0.08);
}

.metric-label {
  font-size: 0.7rem;
  color: var(--text-muted);
  margin-bottom: 0.2rem;
}

.metric-value {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 0.95rem;
}

.text-sky { color: var(--accent-cyan); }
.text-amber { color: var(--accent-amber); }
.text-emerald { color: var(--accent-emerald); }

.sim-footer {
  margin-top: 0.75rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.sim-hint {
  font-size: 0.84rem;
  color: #cbd5e1;
}

/* Practice Problem Cards */
.textbook-problems-section {
  margin: 3.5rem 0;
}

.problem-card {
  background-color: #0e1526;
  border: 1px solid var(--border-color);
  border-radius: 12px;
  margin-bottom: 1.75rem;
  overflow: hidden;
}

.problem-header {
  padding: 1.25rem 1.75rem;
  background-color: #111a2f;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.problem-title-box {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.diff-badge {
  font-size: 0.7rem;
  padding: 0.2rem 0.5rem;
  border-radius: 4px;
  font-weight: 700;
}

.diff-easy { background: rgba(16, 185, 129, 0.2); color: var(--accent-emerald); }
.diff-medium { background: rgba(245, 158, 11, 0.2); color: var(--accent-amber); }
.diff-hard { background: rgba(244, 63, 94, 0.2); color: var(--accent-rose); }

.problem-question-box {
  padding: 1.75rem;
  font-size: 1rem;
  color: #e2e8f0;
  line-height: 1.75;
  border-bottom: 1px solid var(--border-color);
}

.solution-toggle-btn {
  margin: 1.25rem 1.75rem;
  padding: 0.65rem 1.25rem;
  border-radius: 8px;
  font-size: 0.85rem;
  font-weight: 600;
  background-color: #1e293b;
  color: var(--accent-cyan);
  border: 1px solid #334155;
  cursor: pointer;
  transition: all 0.2s;
}

.solution-toggle-btn:hover {
  background-color: #334155;
}

.solution-content {
  display: none;
  padding: 0 1.75rem 1.75rem;
}

.solution-content.open {
  display: block;
}

.solution-step {
  background-color: #0a0f1d;
  border: 1px solid #1e293d;
  border-radius: 8px;
  padding: 1.5rem;
  margin-bottom: 1.25rem;
}

.step-title {
  font-size: 0.88rem;
  font-weight: 700;
  color: var(--accent-emerald);
  margin-bottom: 0.5rem;
}

.step-math {
  margin: 1rem 0;
  overflow-x: auto;
}

.step-explanation {
  font-size: 0.92rem;
  color: var(--text-muted);
  line-height: 1.7;
}

/* Monetization & Google AdSense Placeholders */
.ad-slot-box {
  background-color: #0b0f1a;
  border: 1px dashed #334155;
  border-radius: 8px;
  padding: 0.75rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  position: relative;
  text-align: center;
}

.ad-tag-label {
  font-size: 0.65rem;
  text-transform: uppercase;
  color: #64748b;
  letter-spacing: 0.05em;
  margin-bottom: 0.5rem;
}

.ad-visual-mock {
  width: 100%;
  border-radius: 6px;
  padding: 1.25rem;
  background: linear-gradient(135deg, #1e293b, #0f172a);
  border: 1px solid #334155;
}

.ad-mock-brand {
  font-size: 0.88rem;
  font-weight: 700;
  color: #fff;
  margin-bottom: 0.35rem;
}

.ad-mock-copy {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-bottom: 0.85rem;
  line-height: 1.5;
}

.ad-mock-cta {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 600;
  background-color: var(--accent-cyan);
  color: #090e17;
  padding: 0.4rem 0.9rem;
  border-radius: 4px;
}

.ad-banner-300x600 {
  min-height: 520px;
}

.ad-banner-300x250 {
  min-height: 250px;
}

/* Sticky Bottom Ad Bar */
.bottom-ad-leaderboard {
  position: fixed;
  bottom: 0;
  left: 310px; /* offset sidebar */
  right: 0;
  background: rgba(11, 15, 26, 0.95);
  backdrop-filter: blur(8px);
  border-top: 1px solid var(--border-color);
  padding: 0.5rem 2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1.5rem;
  z-index: 25;
}

.leaderboard-content {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  font-size: 0.82rem;
}

.leaderboard-badge {
  font-size: 0.65rem;
  background-color: #334155;
  color: #cbd5e1;
  padding: 0.15rem 0.4rem;
  border-radius: 3px;
}

/* 1-Hour Rewarded Ad Modal */
.ad-modal-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background-color: rgba(0, 0, 0, 0.88);
  backdrop-filter: blur(10px);
  z-index: 100;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
}

.ad-modal-overlay.open {
  display: flex;
}

.ad-modal-card {
  background-color: #111827;
  border: 1px solid #38bdf8;
  border-radius: 16px;
  max-width: 580px;
  width: 100%;
  padding: 2.25rem;
  text-align: center;
  box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.7);
}

.ad-modal-icon {
  font-size: 3rem;
  margin-bottom: 0.75rem;
}

.ad-modal-title {
  font-size: 1.5rem;
  font-weight: 800;
  color: #fff;
  margin-bottom: 0.5rem;
}

.ad-modal-desc {
  font-size: 0.92rem;
  color: var(--text-muted);
  margin-bottom: 1.5rem;
}

.ad-video-mockup {
  background-color: #000;
  border-radius: 8px;
  padding: 2rem 1rem;
  border: 1px solid #334155;
  margin-bottom: 1.5rem;
  position: relative;
}

.ad-countdown-timer {
  font-size: 1.8rem;
  font-family: var(--font-mono);
  font-weight: 700;
  color: var(--accent-amber);
  margin-bottom: 0.5rem;
}

.btn-resume-study {
  width: 100%;
  padding: 0.85rem;
  border-radius: 8px;
  font-size: 0.95rem;
  font-weight: 700;
  background-color: var(--accent-emerald);
  color: #064e3b;
  border: none;
  cursor: pointer;
  transition: opacity 0.2s;
}

.btn-resume-study:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

/* Responsive adjustments */
@media (max-width: 1120px) {
  .ads-sidebar-column {
    display: none;
  }
  .bottom-ad-leaderboard {
    left: 0;
  }
}

@media (max-width: 768px) {
  .sidebar {
    display: none;
  }
  .content-columns {
    padding: 1.25rem;
  }
}

/* Textbook Reader Bottom Trust & Navigation Footer */
.reader-trust-footer {
  margin-top: 4rem;
  padding: 2.5rem 1.5rem 2rem;
  border-top: 1px solid var(--border-color);
  text-align: center;
  color: var(--text-muted);
}

.reader-trust-links {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 1.5rem;
  margin-bottom: 1rem;
}

.reader-trust-link {
  color: #94a3b8;
  text-decoration: none;
  font-size: 0.88rem;
  font-weight: 500;
  transition: color 0.15s ease;
}

.reader-trust-link:hover {
  color: var(--accent-cyan);
}

.reader-trust-link.active-trust-link {
  color: var(--accent-cyan);
  font-weight: 600;
}

.reader-trust-copy {
  font-size: 0.8rem;
  color: #64748b;
  margin-top: 0.35rem;
}