/* JetBrains Mono */
@font-face {
  font-family: 'Local JetBrains Mono';
  font-style: normal;
  font-weight: 400 700;
  font-display: swap;
  src: url('../fonts/jetbrains-mono-v24-latin-regular.woff2') format('woff2');
}

/* Lora */
@font-face {
  font-family: 'Local Lora';
  font-style: normal;
  font-weight: 400 700;
  font-display: swap;
  src: url('../fonts/lora-v37-latin-regular.woff2') format('woff2');
}

/* Source Serif 4 */
@font-face {
  font-family: 'Local Source Serif 4';
  font-style: normal;
  font-weight: 300 900; 
  font-display: swap;
  src: url('../fonts/source-serif-4-v14-latin-regular.woff2') format('woff2');
}

:root {
  --bg-base: #f0e9dc;
  --bg-surface: #e8dfd0;
  --bg-elevated: #ddd3c0;
  --bg-code: black;
  --bg-code-header: #232522;
  --bg-sidebar: #ede6d8;

  --border: #c8b89e;
  --border-soft: #d8cbb5;
  --border-strong: #b0a08a;

  --text-ink: #1e1810;
  --text-body: #3a3020;
  --text-muted: #645845;
  --text-dim: #8d795f;
  --text-code: #f0e9dc;

  --sky: #4a8fa8;
  --sky-light: #6baec7;
  --sky-dim: rgba(74, 143, 168, 0.12);
  --sky-glow: rgba(74, 143, 168, 0.06);

  --sage: #5c8a58;
  --sage-dim: rgba(92, 138, 88, 0.12);

  --terra: #b85c2a;
  --terra-dim: rgba(184, 92, 42, 0.11);

  --amber: #c4891a;
  --amber-dim: rgba(196, 137, 26, 0.11);

  /* Using local font families with fallbacks if needed */
  --font-display: 'Local Lora', 'Lora', Georgia, serif;
  --font-body: 'Local Source Serif 4', 'Source Serif 4', Georgia, serif;
  --font-mono: 'Local JetBrains Mono', 'JetBrains Mono', 'Fira Code', monospace;
}

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

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

body {
  background-color: var(--bg-base);
  color: var(--text-body);
  font-family: var(--font-body);
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}

a {
  text-decoration: none;
  color: inherit;
}

.font-display {
  font-family: var(--font-display);
}

.font-mono {
  font-family: var(--font-mono);
}

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

/* ── Scrollbar ── */
::-webkit-scrollbar {
  width: 5px;
  height: 5px;
}

::-webkit-scrollbar-track {
  background: var(--bg-surface);
}

::-webkit-scrollbar-thumb {
  background: var(--border-strong);
  border-radius: 3px;
}

/* ── Grid texture ── */
.grid-bg {
  background-image:
    linear-gradient(var(--border-soft) 1px, transparent 1px),
    linear-gradient(90deg, var(--border-soft) 1px, transparent 1px);
  background-size: 40px 40px;
}

.text-gradient {
  background: linear-gradient(135deg, #4a8fa8 0%, #5c8a58 55%, #c4891a 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ═══ NAVBAR ═══ */
#navbar {
  background-color: rgba(240, 233, 220, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}

.nav-link {
  display: inline-block;
  padding: 0.4rem 0.85rem;
  border-radius: 0.5rem;
  font-size: 0.875rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
  transition: color 0.15s, background-color 0.15s;
}

.nav-link:hover,
.nav-link.active {
  color: var(--text-ink);
  background-color: var(--bg-elevated);
}

.mobile-nav-link {
  display: block;
  padding: 0.6rem 0.85rem;
  border-radius: 0.5rem;
  font-size: 0.875rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
  transition: color 0.15s, background-color 0.15s;
}

.mobile-nav-link:hover {
  color: var(--text-ink);
  background-color: var(--bg-elevated);
}

/* Mobile menu bg */
#mobile-menu {
  background-color: rgba(240, 233, 220, 0.98);
  border-top: 1px solid var(--border);
}

/* ═══ BUTTONS ═══ */
.btn-primary {
  display: inline-flex;
  align-items: center;
  padding: 0.75rem 1.75rem;
  background-color: var(--sky);
  color: #f0e9dc;
  font-size: 0.875rem;
  font-weight: 600;
  font-family: var(--font-mono);
  border-radius: 0.625rem;
  border: 2px solid var(--sky);
  transition: background-color 0.15s, transform 0.1s, box-shadow 0.15s;
  box-shadow: 0 2px 12px rgba(74, 143, 168, 0.22);
}

.btn-primary:hover {
  background-color: var(--sky-light);
  border-color: var(--sky-light);
  transform: translateY(-1px);
  box-shadow: 0 4px 20px rgba(74, 143, 168, 0.32);
}

.btn-secondary {
  display: inline-flex;
  align-items: center;
  padding: 0.75rem 1.75rem;
  background-color: transparent;
  color: var(--text-muted);
  font-size: 0.875rem;
  font-weight: 500;
  font-family: var(--font-mono);
  border-radius: 0.625rem;
  border: 2px solid var(--border-strong);
  transition: color 0.15s, border-color 0.15s, background-color 0.15s;
}

.btn-secondary:hover {
  color: var(--text-ink);
  border-color: var(--sky);
  background-color: var(--sky-glow);
}

/* ═══ HOME COMPONENTS ═══ */
.module-card {
  display: flex;
  gap: 1.25rem;
  padding: 1.5rem;
  background-color: var(--bg-surface);
  border: 1.5px solid var(--border);
  border-radius: 1rem;
  transition: border-color 0.2s, box-shadow 0.2s, transform 0.15s;
}

.module-card:hover {
  border-color: var(--sky);
  box-shadow: 0 4px 20px rgba(74, 143, 168, 0.1);
  transform: translateY(-2px);
}

.module-number {
  flex-shrink: 0;
  width: 2.5rem;
  height: 2.5rem;
  border-radius: 0.5rem;
  background-color: var(--bg-elevated);
  border: 1px solid var(--border-strong);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  color: var(--text-muted);
  font-weight: 700;
  letter-spacing: 0.04em;
}

.tag {
  display: inline-block;
  padding: 0.2rem 0.6rem;
  background-color: var(--bg-elevated);
  border: 1px solid var(--border-strong);
  border-radius: 9999px;
  font-size: 0.7rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
}

.feature-icon {
  width: 2.75rem;
  height: 2.75rem;
  border-radius: 0.625rem;
  border: 1.5px solid var(--border-strong);
  background-color: var(--bg-elevated);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
  color: var(--sky);
  font-family: var(--font-mono);
  font-weight: bold;
}

/* ═══ LESSON LAYOUT ═══ */
.lesson-sidebar {
  width: 256px;
  flex-shrink: 0;
  border-right: 1px solid var(--border);
  background-color: var(--bg-sidebar);
  display: none;
}

@media (min-width: 1024px) {
  .lesson-sidebar {
    display: block;
  }
}

@media (max-width: 1023px) {
  .lesson-sidebar {
    display: block;
    position: fixed;
    top: 4rem;
    left: 0;
    bottom: 0;
    z-index: 40;
    transform: translateX(-100%);
    transition: transform 0.28s cubic-bezier(0.4, 0, 0.2, 1);
    overflow-y: auto;
  }

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

.lesson-main {
  flex: 1;
  min-width: 0;
  background-color: var(--bg-base);
}

.toc-sidebar {
  width: 210px;
  flex-shrink: 0;
  border-left: 1px solid var(--border);
  background-color: var(--bg-sidebar);
  display: none;
}

@media (min-width: 1280px) {
  .toc-sidebar {
    display: block;
  }
}

/* Sidebar internals */
.sidebar-module {
  margin-bottom: 0.2rem;
}

.sidebar-module-btn {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  width: 100%;
  padding: 0.5rem 0.625rem;
  border-radius: 0.5rem;
  font-size: 0.78rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
  background: transparent;
  border: none;
  cursor: pointer;
  text-align: left;
  transition: color 0.15s, background-color 0.15s;
}

.sidebar-module-btn:hover {
  color: var(--text-ink);
  background-color: var(--bg-elevated);
}

.sidebar-module-num {
  font-size: 0.65rem;
  color: var(--text-dim);
  flex-shrink: 0;
  font-weight: 700;
}

.sidebar-lesson-list {
  padding-left: 2.2rem;
  margin: 0.2rem 0 0.5rem;
}

.sidebar-lesson {
  display: block;
  padding: 0.3rem 0.5rem;
  font-size: 0.77rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
  border-radius: 0.375rem;
  transition: color 0.15s, background-color 0.15s;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  line-height: 1.45;
}

.sidebar-lesson:hover {
  color: var(--text-ink);
  background-color: var(--bg-elevated);
}

.sidebar-lesson.active {
  color: var(--sky);
  background-color: var(--sky-dim);
  font-weight: 600;
}

/* ToC */
.toc-list {
  list-style: none;
  padding: 0;
}

.toc-sublist {
  list-style: none;
  padding-left: 0.875rem;
}

.toc-link {
  display: block;
  padding: 0.3rem 0.5rem 0.3rem 0.75rem;
  font-size: 0.77rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
  border-radius: 0.25rem;
  border-left: 2px solid transparent;
  line-height: 1.4;
  transition: color 0.15s, border-color 0.15s, background-color 0.15s;
}

.toc-link:hover {
  color: var(--text-ink);
}

.toc-link.active {
  color: var(--sky);
  border-left-color: var(--sky);
  background-color: var(--sky-dim);
}

.toc-link--sub {
  font-size: 0.72rem;
}

/* Badges */
.lesson-badge {
  display: inline-flex;
  align-items: center;
  padding: 0.2rem 0.625rem;
  border: 1px solid var(--border-strong);
  background-color: var(--bg-elevated);
  border-radius: 9999px;
  font-size: 0.7rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
}

.lesson-badge--beginner {
  border-color: rgba(92, 138, 88, 0.4);
  background-color: var(--sage-dim);
  color: #3a6536;
}

.lesson-badge--intermediate {
  border-color: rgba(196, 137, 26, 0.4);
  background-color: var(--amber-dim);
  color: #7a5510;
}

/* ═══ LESSON PROSE ═══ */
.lesson-prose {
  font-family: var(--font-body);
  font-size: 1.0625rem;
  line-height: 1.85;
  color: var(--text-body);
}

.lesson-prose h2 {
  font-family: var(--font-display);
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--text-ink);
  margin-top: 3rem;
  margin-bottom: 1rem;
  padding-bottom: 0.6rem;
  border-bottom: 1.5px solid var(--border);
  scroll-margin-top: 5rem;
}

.lesson-prose h3 {
  font-family: var(--font-display);
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text-ink);
  margin-top: 2rem;
  margin-bottom: 0.6rem;
  scroll-margin-top: 5rem;
}

.lesson-prose p {
  margin-bottom: 1.2rem;
}

.lesson-prose strong {
  color: var(--text-ink);
  font-weight: 700;
}

.lesson-prose em {
  font-style: italic;
}

.lesson-prose a {
  color: var(--sky);
  text-decoration: underline;
  text-decoration-color: rgba(74, 143, 168, 0.35);
  text-underline-offset: 3px;
  transition: color 0.15s;
}

.lesson-prose a:hover {
  color: var(--sky-light);
}

.lesson-prose code {
  font-family: var(--font-mono);
  font-size: 0.875em;
  background-color: black;
  /* border: 1px solid var(--border-strong); */
  padding: 0.15em 0.4em;
  border-radius: 0.25rem;
  color: var(--terra);
}

.lesson-prose blockquote {
  border-left: 3px solid var(--sky);
  padding: 0.875rem 1.25rem;
  margin: 1.75rem 0;
  background-color: var(--sky-dim);
  border-radius: 0 0.5rem 0.5rem 0;
  font-style: italic;
  color: var(--text-muted);
}

.lesson-list {
  list-style: none;
  margin: 1.25rem 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.lesson-prose ol.lesson-list {
  counter-reset: lesson-counter;
}

.lesson-prose ol.lesson-list li {
  counter-increment: lesson-counter;
  display: flex;
  gap: 1rem;
  padding: 0.625rem 1rem;
  background-color: var(--bg-surface);
  border: 1px solid var(--border-soft);
  border-radius: 0.5rem;
}

.lesson-prose ol.lesson-list li::before {
  content: counter(lesson-counter, decimal-leading-zero);
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--sky);
  flex-shrink: 0;
  padding-top: 0.15rem;
  min-width: 1.75rem;
  font-weight: 700;
}

.lesson-prose ul.lesson-list li {
  display: flex;
  gap: 0.75rem;
  align-items: flex-start;
}

.lesson-prose ul.lesson-list li::before {
  content: '›';
  color: var(--sky);
  font-size: 1.15em;
  flex-shrink: 0;
  line-height: 1.65;
  font-weight: bold;
}

/* ═══ MATH BLOCKS ═══ */
.math-block {
  margin: 2rem 0;
  padding: 1.5rem 2rem;
  background-color: var(--bg-surface);
  border: 1.5px solid var(--border);
  border-left: 4px solid var(--sky);
  border-radius: 0 0.75rem 0.75rem 0;
  overflow-x: auto;
  text-align: center;
}

.math-block .katex-display {
  margin: 0.5rem 0;
  overflow-x: auto;
}

.math-label {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  color: var(--sky);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.75rem;
  display: block;
}

.math-caption {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-top: 0.75rem;
  font-style: italic;
  display: block;
}

/* ═══ CODE BLOCKS ═══ */
.code-block {
  margin: 1.75rem 0;
  border: 1.5px solid var(--border-strong);
  border-radius: 0.75rem;
  overflow: hidden;
  background-color: var(--bg-code);
}

.code-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.6rem 1rem;
  background-color: var(--bg-code-header);
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
}

.code-lang {
  font-family: var(--font-mono);
  font-size: 0.67rem;
  color: rgba(240, 233, 220, 0.4);
  text-transform: uppercase;
  letter-spacing: 0.12em;
}

.copy-btn {
  font-family: var(--font-mono);
  font-size: 0.67rem;
  color: rgba(240, 233, 220, 0.38);
  background: transparent;
  border: 1px solid rgba(255, 255, 255, 0.11);
  padding: 0.2rem 0.6rem;
  border-radius: 0.25rem;
  cursor: pointer;
  transition: color 0.15s, border-color 0.15s;
}

.copy-btn:hover {
  color: var(--sky-light);
  border-color: rgba(107, 174, 199, 0.6);
}

.copy-btn.copied {
  color: #7ec87e;
}

.code-block pre {
  margin: 0 !important;
  padding: 1.25rem !important;
  background: transparent !important;
  font-family: var(--font-mono) !important;
  font-size: 0.875rem !important;
  line-height: 1.65 !important;
  overflow-x: auto;
}

.code-block pre code {
  font-family: var(--font-mono) !important;
}

pre[class*="language-"] {
  background: transparent !important;
}

code[class*="language-"] {
  font-family: var(--font-mono) !important;
}

/* ═══ CALLOUTS ═══ */
.callout {
  display: flex;
  gap: 1rem;
  padding: 1rem 1.25rem;
  border-radius: 0.625rem;
  margin: 1.75rem 0;
  font-size: 0.9375rem;
  line-height: 1.65;
}

.callout-icon {
  font-size: 1.05rem;
  flex-shrink: 0;
  padding-top: 0.05rem;
}

.callout--info {
  background-color: var(--sky-dim);
  border: 1px solid rgba(74, 143, 168, 0.3);
  color: #2e6578;
}

.callout--info strong {
  color: #1d4d5e;
}

.callout--warning {
  background-color: var(--terra-dim);
  border: 1px solid rgba(184, 92, 42, 0.3);
  color: #8b3a14;
}

.callout--warning strong {
  color: #6b2a0a;
}

.callout--tip {
  background-color: var(--sage-dim);
  border: 1px solid rgba(92, 138, 88, 0.3);
  color: #385835;
}

.callout--tip strong {
  color: #274a24;
}

/* ═══ DEFINITION LIST ═══ */
.def-list {
  margin: 1.5rem 0;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.def-row {
  display: flex;
  gap: 1rem;
  padding: 0.75rem 1rem;
  background-color: var(--bg-surface);
  border: 1px solid var(--border-soft);
  border-radius: 0.5rem;
  align-items: flex-start;
}

.def-term {
  font-family: var(--font-mono);
  font-size: 0.77rem;
  color: var(--sky);
  flex-shrink: 0;
  min-width: 7.5rem;
  padding-top: 0.12rem;
  font-weight: 700;
  letter-spacing: 0.02em;
}

.def-desc {
  font-size: 0.9375rem;
  color: var(--text-body);
}

/* ═══ COMPARISON GRID ═══ */
.comparison-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1px;
  background-color: var(--border);
  border: 1.5px solid var(--border);
  border-radius: 0.75rem;
  overflow: hidden;
  margin: 1.75rem 0;
}

.comparison-col {
  background-color: var(--bg-surface);
  padding: 1.25rem;
}

@media (max-width: 600px) {
  .comparison-grid {
    grid-template-columns: 1fr;
  }
}

/* ═══ PREV/NEXT ═══ */
.prev-next-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 1.5px solid var(--border);
}

.prev-next-btn {
  display: flex;
  align-items: center;
  gap: 0.875rem;
  padding: 1rem 1.25rem;
  background-color: var(--bg-surface);
  border: 1.5px solid var(--border);
  border-radius: 0.75rem;
  color: var(--text-body);
  transition: border-color 0.15s, background-color 0.15s;
}

.prev-next-btn:hover:not(.prev-next-btn--disabled) {
  border-color: var(--sky);
  background-color: var(--sky-glow);
}

.prev-next-btn--disabled {
  opacity: 0.3;
  cursor: default;
  pointer-events: none;
}

.prev-next-btn:last-child {
  justify-content: flex-end;
}

@media (max-width: 640px) {
  .prev-next-nav {
    grid-template-columns: 1fr;
  }
}

/* ═══ ANIMATIONS ═══ */
@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(14px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.fade-up {
  animation: fadeUp 0.4s ease both;
}

.delay-100 {
  animation-delay: 0.10s;
}

.delay-200 {
  animation-delay: 0.20s;
}

.delay-300 {
  animation-delay: 0.30s;
}

.delay-400 {
  animation-delay: 0.40s;
}

/* ═══ FOOTER ═══ */
footer {
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border);
}

/* ----------------------------- */


#back-to-top {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  width: 2.75rem;
  height: 2.75rem;
  border-radius: 50%;
  background: var(--bg-surface);
  border: 1px solid var(--border);
  color: var(--text-muted);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 0.2s, transform 0.2s, border-color 0.2s;
  z-index: 48;
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.08);
}

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

#back-to-top:hover {
  border-color: var(--sky);
  color: var(--sky);
}