/* ============================================================
   CUSTOM PROPERTIES
   ============================================================ */
:root {
  /* Sidebar */
  --sidebar-w: 300px;
  --sidebar-bg: #111318;
  --sidebar-bg-2: #17191f;
  --sidebar-border: #1f2229;
  --sidebar-text: #dde1e7;
  --sidebar-muted: #737d8c;
  --sidebar-active-bg: #1e2530;
  --sidebar-active-border: #6366f1;

  /* Status colors */
  --green: #22c55e;
  --green-soft: #16a34a;
  --indigo: #6366f1;

  /* Content (light) */
  --bg: #f8f9fb;
  --surface: #ffffff;
  --text: #111827;
  --text-2: #374151;
  --text-muted: #6b7280;
  --border: #e5e7eb;
  --link: #2563eb;
  --topbar-bg: #ffffff;
  --pill-bg: #f3f4f6;
  --pro-bg: #ede9fe;
  --pro-text: #6d28d9;

  /* Code / body */
  --body-bg: #ffffff;
  --body-text: #1f2937;
  --body-muted: #6b7280;
  --body-border: #e5e7eb;
  --code-bg: #f6f8fa;
  --code-text: #1f2937;
  --code-inline-bg: #f0f0f0;
  --code-inline-text: #c0392b;
  --blockquote-bg: #faf5ff;
  --blockquote-border: #c084fc;
  --blockquote-text: #581c87;
  --tab-header-bg: #f9fafb;

  /* Shadows */
  --shadow-xs: 0 1px 2px rgba(0,0,0,0.04);
  --shadow-sm: 0 1px 4px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.08), 0 2px 4px rgba(0,0,0,0.04);

  /* Transitions */
  --t-fast: 120ms ease;
  --t-med: 200ms ease;
  --t-slow: 320ms ease;
}

/* ============================================================
   DARK MODE
   ============================================================ */
body.theme-dark {
  --bg: #0d1117;
  --surface: #161b22;
  --text: #e6edf3;
  --text-2: #c9d1d9;
  --text-muted: #8b949e;
  --border: #30363d;
  --link: #58a6ff;
  --topbar-bg: #161b22;
  --pill-bg: #21262d;
  --pro-bg: #2d1f5e;
  --pro-text: #c4b5fd;

  --body-bg: #0d1117;
  --body-text: #e6edf3;
  --body-muted: #8b949e;
  --body-border: #30363d;
  --code-bg: #161b22;
  --code-text: #e6edf3;
  --code-inline-bg: #21262d;
  --code-inline-text: #f97316;
  --blockquote-bg: #1a1040;
  --blockquote-border: #7c3aed;
  --blockquote-text: #c4b5fd;
  --tab-header-bg: #161b22;

  --shadow-xs: 0 1px 2px rgba(0,0,0,0.3);
  --shadow-sm: 0 1px 4px rgba(0,0,0,0.4), 0 1px 2px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.5), 0 2px 4px rgba(0,0,0,0.3);
}

/* ============================================================
   KEYFRAME ANIMATIONS
   ============================================================ */
@keyframes fadeUp {
  from { opacity: 0; transform: translateY(14px); }
  to   { opacity: 1; transform: translateY(0); }
}
@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}
@keyframes spin {
  to { transform: rotate(360deg); }
}
@keyframes shimmer {
  0%   { background-position: -600px 0; }
  100% { background-position: 600px 0; }
}
@keyframes slideInLeft {
  from { opacity: 0; transform: translateX(-8px); }
  to   { opacity: 1; transform: translateX(0); }
}
@keyframes progressPulse {
  0%, 100% { opacity: 1; }
  50%       { opacity: 0.6; }
}

/* ============================================================
   RESET / BASE
   ============================================================ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Inter", "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 14px;
  line-height: 1.5;
  color: var(--text);
  background: var(--bg);
  min-height: 100vh;
  transition: background var(--t-med), color var(--t-med);
}

a { color: var(--link); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ============================================================
   TOP BAR
   ============================================================ */
.topbar {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 56px;
  padding: 0 20px;
  background: var(--topbar-bg);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(8px);
  transition: background var(--t-med), border-color var(--t-med);
}
.topbar-left { display: flex; align-items: center; gap: 16px; }

.logo {
  width: 32px; height: 32px;
  display: flex; align-items: center; justify-content: center;
  border-radius: 8px;
  transition: opacity var(--t-fast);
}
.logo:hover { opacity: 0.8; }

.topnav { display: flex; gap: 2px; }
.topnav a {
  padding: 6px 12px;
  border-radius: 7px;
  color: var(--text-muted);
  font-weight: 500;
  font-size: 13.5px;
  transition: background var(--t-fast), color var(--t-fast);
}
.topnav a:hover { background: var(--pill-bg); color: var(--text); text-decoration: none; }
.topnav a.active { background: var(--pill-bg); color: var(--text); }

.topbar-right { display: flex; align-items: center; gap: 10px; }

.course-select {
  height: 32px;
  padding: 0 28px 0 10px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 13px;
  cursor: pointer;
  appearance: none;
  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 24 24'><path fill='%236b7280' d='M7 10l5 5 5-5z'/></svg>");
  background-repeat: no-repeat;
  background-position: right 8px center;
  max-width: 260px;
  transition: border-color var(--t-fast), box-shadow var(--t-fast);
}
.course-select:hover { border-color: var(--indigo); }
.course-select:focus { outline: none; border-color: var(--indigo); box-shadow: 0 0 0 3px rgba(99,102,241,0.15); }
body.theme-dark .course-select {
  background-color: var(--pill-bg);
  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 24 24'><path fill='%238b949e' d='M7 10l5 5 5-5z'/></svg>");
}

.pro-pill {
  padding: 3px 9px;
  font-size: 11.5px;
  font-weight: 700;
  background: var(--pro-bg);
  color: var(--pro-text);
  border-radius: 999px;
  letter-spacing: 0.02em;
}

.icon-btn {
  width: 32px; height: 32px;
  border: 0;
  background: transparent;
  color: var(--text-muted);
  border-radius: 8px;
  cursor: pointer;
  display: inline-flex; align-items: center; justify-content: center;
  transition: background var(--t-fast), color var(--t-fast), transform var(--t-fast);
}
.icon-btn:hover { background: var(--pill-bg); color: var(--text); }
.icon-btn:active { transform: scale(0.92); }

.avatar {
  width: 28px; height: 28px;
  border-radius: 50%;
  background: linear-gradient(135deg, #fbbf24, #f97316);
  box-shadow: 0 0 0 2px var(--border);
  cursor: pointer;
  transition: box-shadow var(--t-fast), transform var(--t-fast);
}
.avatar:hover { box-shadow: 0 0 0 2px var(--indigo); transform: scale(1.05); }

/* Mobile sidebar toggle */
.sidebar-toggle {
  display: none;
  width: 32px; height: 32px;
  border: 0;
  background: transparent;
  color: var(--text-muted);
  border-radius: 8px;
  cursor: pointer;
  align-items: center; justify-content: center;
  transition: background var(--t-fast);
}
.sidebar-toggle:hover { background: var(--pill-bg); color: var(--text); }

/* ============================================================
   LAYOUT
   ============================================================ */
.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) 1fr;
  min-height: calc(100vh - 56px);
}

/* ============================================================
   SIDEBAR
   ============================================================ */
.sidebar {
  background: var(--sidebar-bg);
  color: var(--sidebar-text);
  border-right: 1px solid var(--sidebar-border);
  position: sticky;
  top: 56px;
  align-self: start;
  height: calc(100vh - 56px);
  overflow-y: auto;
  overflow-x: hidden;
  scrollbar-width: thin;
  scrollbar-color: #2e333d transparent;
  transition: transform var(--t-slow);
  will-change: transform;
}
.sidebar::-webkit-scrollbar { width: 4px; }
.sidebar::-webkit-scrollbar-track { background: transparent; }
.sidebar::-webkit-scrollbar-thumb { background: #2e333d; border-radius: 4px; }

.sidebar-header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 16px;
  border-bottom: 1px solid var(--sidebar-border);
  position: sticky;
  top: 0;
  background: var(--sidebar-bg);
  z-index: 5;
}

/* Progress ring */
.progress-ring { position: relative; width: 40px; height: 40px; flex: 0 0 auto; }
.progress-ring svg { width: 100%; height: 100%; transform: rotate(-90deg); }
.progress-ring .ring-bg { fill: none; stroke: #242830; stroke-width: 3; }
.progress-ring .ring-fg {
  fill: none; stroke: var(--green); stroke-width: 3;
  stroke-linecap: round;
  transition: stroke-dasharray 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}
.progress-ring span {
  position: absolute; inset: 0;
  display: flex; align-items: center; justify-content: center;
  font-size: 10px; font-weight: 700;
  color: var(--sidebar-text);
}

.course-title {
  flex: 1; min-width: 0;
  display: flex; align-items: center; justify-content: space-between; gap: 8px;
  font-weight: 600; font-size: 13px; line-height: 1.3;
  color: var(--sidebar-text);
}
.course-title span { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.course-title .chev { flex-shrink: 0; color: var(--sidebar-muted); }

.sections { padding: 4px 0 80px; }

/* Section group */
.section { border-bottom: 1px solid var(--sidebar-border); }
.section-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 10px 16px;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--sidebar-muted);
  cursor: pointer;
  user-select: none;
  background: var(--sidebar-bg-2);
  transition: color var(--t-fast);
}
.section-header:hover { color: var(--sidebar-text); }
.section-header .chev { transition: transform var(--t-med); color: var(--sidebar-muted); }
.section.collapsed .section-header .chev { transform: rotate(-90deg); }

.section-list { list-style: none; }
.section.collapsed .section-list { display: none; }

/* Lesson row */
.lesson {
  display: grid;
  grid-template-columns: 26px 1fr auto;
  align-items: center;
  gap: 8px;
  padding: 8px 14px 8px 12px;
  cursor: pointer;
  border-left: 3px solid transparent;
  transition: background var(--t-fast), border-color var(--t-fast);
}
.lesson:hover { background: rgba(255,255,255,0.04); }
.lesson.active {
  background: var(--sidebar-active-bg);
  border-left-color: var(--sidebar-active-border);
}
.lesson.active .lesson-title-text { color: #fff; }

.lesson-num {
  color: var(--sidebar-muted);
  font-size: 11.5px;
  text-align: right;
  font-variant-numeric: tabular-nums;
}
.lesson-title-text {
  display: flex; align-items: center; gap: 6px;
  font-size: 13px; font-weight: 500; color: var(--sidebar-text);
  line-height: 1.3;
  overflow: hidden;
}
.lesson-title-text-inner {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.lesson-check { color: var(--green); font-size: 12px; flex-shrink: 0; }
.lesson-meta { display: flex; align-items: center; gap: 4px; flex-shrink: 0; }

.pill {
  border: 1px solid rgba(255,255,255,0.1);
  border-radius: 5px;
  padding: 1px 5px;
  font-size: 10.5px;
  color: var(--sidebar-muted);
  white-space: nowrap;
}
.pill.free { border-color: var(--green-soft); color: var(--green); }

/* Loading skeleton in sidebar */
.lesson-skeleton {
  height: 38px;
  padding: 8px 14px 8px 12px;
}
.skeleton-line {
  height: 10px;
  border-radius: 5px;
  background: linear-gradient(90deg, #1f2229 25%, #262b34 50%, #1f2229 75%);
  background-size: 600px 100%;
  animation: shimmer 1.4s infinite;
}

/* ============================================================
   CONTENT AREA
   ============================================================ */
.content {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 256px;
  background: var(--bg);
  min-width: 0;
  transition: background var(--t-med);
}
.content-inner {
  padding: 24px 28px 80px;
  min-width: 0;
  width: 100%;
  max-width: 900px;
}

/* Lesson heading row */
.lesson-title-row {
  display: flex; align-items: flex-start; justify-content: space-between;
  margin-bottom: 16px;
  animation: fadeUp 0.3s ease both;
}
.lesson-title-row h2 {
  font-size: 22px;
  font-weight: 700;
  color: var(--text);
  line-height: 1.3;
}

/* ---- Video ---- */
.video-wrap {
  background: #000;
  border-radius: 10px;
  overflow: hidden;
  aspect-ratio: 16 / 9;
  width: 100%;
  box-shadow: var(--shadow-md);
  animation: fadeIn 0.35s ease both;
  transition: box-shadow var(--t-med);
}
.video-wrap:hover { box-shadow: 0 8px 24px rgba(0,0,0,0.15); }
.video-wrap video { width: 100%; height: 100%; display: block; }
.video-wrap.hidden { display: none; }

/* ---- Actions bar ---- */
.actions-bar {
  display: flex; align-items: center; justify-content: space-between;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 14px;
  margin-top: 14px;
  box-shadow: var(--shadow-xs);
  animation: fadeUp 0.35s 0.05s ease both;
  transition: background var(--t-med), border-color var(--t-med);
}
.mark-complete {
  display: inline-flex; align-items: center; gap: 8px;
  cursor: pointer; user-select: none; font-size: 13px; color: var(--text-muted);
  transition: color var(--t-fast);
}
.mark-complete:hover { color: var(--text); }
.mark-complete input[type="checkbox"] {
  width: 16px; height: 16px; cursor: pointer; accent-color: var(--green);
}
.actions-right { display: flex; gap: 6px; align-items: center; }

.ghost-btn, .nav-btn {
  height: 30px;
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: 7px;
  font-size: 13px;
  padding: 0 10px;
  cursor: pointer;
  color: var(--text-muted);
  display: inline-flex; align-items: center; gap: 6px;
  transition: background var(--t-fast), color var(--t-fast), border-color var(--t-fast), transform var(--t-fast);
}
.ghost-btn:hover, .nav-btn:hover {
  background: var(--pill-bg);
  color: var(--text);
  border-color: var(--indigo);
}
.ghost-btn:active, .nav-btn:active { transform: scale(0.95); }
.nav-btn { width: 30px; padding: 0; justify-content: center; }
.ghost-btn code-icon { font-family: ui-monospace, monospace; color: var(--text-muted); }

/* ---- Star rating ---- */
.rate {
  display: flex; gap: 10px; align-items: center;
  padding: 8px 2px; color: var(--text-muted); font-size: 13px;
  animation: fadeUp 0.35s 0.1s ease both;
}
.stars { display: inline-flex; gap: 1px; cursor: pointer; }
.stars span {
  color: #d1d5db;
  font-size: 20px;
  line-height: 1;
  transition: color var(--t-fast), transform var(--t-fast);
}
.stars span:hover,
.stars span:hover ~ span { transform: scale(1.15); }
.stars span.on { color: #fbbf24; }

/* ---- Loading spinner ---- */
.lesson-loading {
  display: flex; align-items: center; justify-content: center;
  padding: 60px 0;
  animation: fadeIn 0.2s ease both;
}
.spinner {
  width: 32px; height: 32px;
  border: 3px solid var(--border);
  border-top-color: var(--indigo);
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
}

/* ---- Lesson body skeleton ---- */
.body-skeleton {
  margin-top: 18px;
  animation: fadeIn 0.2s ease both;
}
.body-skeleton .sk-block {
  height: 14px; border-radius: 6px; margin: 12px 0;
  background: linear-gradient(90deg, var(--border) 25%, var(--pill-bg) 50%, var(--border) 75%);
  background-size: 600px 100%;
  animation: shimmer 1.4s infinite;
}
.body-skeleton .sk-block.wide   { width: 100%; }
.body-skeleton .sk-block.medium { width: 70%; }
.body-skeleton .sk-block.short  { width: 45%; }
.body-skeleton .sk-block.title  { width: 55%; height: 22px; margin-bottom: 18px; }

/* ============================================================
   LESSON BODY  — injected HTML from individual .html files
   ============================================================ */
.lesson-body {
  background: var(--body-bg);
  border: 1px solid var(--body-border);
  border-radius: 12px;
  padding: 28px 32px 40px;
  margin-top: 18px;
  box-shadow: var(--shadow-sm);
  font-size: 15px;
  line-height: 1.75;
  color: var(--body-text);
  transition: background var(--t-med), border-color var(--t-med), box-shadow var(--t-med);
  animation: fadeUp 0.35s 0.05s ease both;
}

/* Headings */
.lesson-body h1 {
  font-size: 26px; font-weight: 700; line-height: 1.25;
  margin: 4px 0 20px;
  padding-bottom: 14px;
  border-bottom: 1px solid var(--body-border);
  color: var(--body-text);
}
.lesson-body h2 {
  font-size: 19px; font-weight: 700; line-height: 1.3;
  margin: 34px 0 10px;
  color: var(--body-text);
}
.lesson-body h3 {
  font-size: 16px; font-weight: 600; line-height: 1.35;
  margin: 24px 0 8px;
  color: var(--body-text);
}
.lesson-body h4 { font-size: 15px; font-weight: 600; margin: 18px 0 6px; }

/* Paragraphs */
.lesson-body p { margin: 10px 0; }
.lesson-body strong { font-weight: 700; }
.lesson-body em { font-style: italic; }
.lesson-body hr { border: 0; border-top: 1px solid var(--body-border); margin: 28px 0; }

/* Lists */
.lesson-body ul, .lesson-body ol { padding-left: 26px; margin: 8px 0 12px; }
.lesson-body li { margin: 5px 0; line-height: 1.65; }
.lesson-body li > ul, .lesson-body li > ol { margin: 4px 0; }

/* Links */
.lesson-body a { color: var(--link); transition: opacity var(--t-fast); }
.lesson-body a:hover { opacity: 0.8; }

/* Blockquotes */
.lesson-body blockquote {
  border-left: 4px solid var(--blockquote-border);
  background: var(--blockquote-bg);
  margin: 18px 0;
  padding: 12px 18px;
  border-radius: 0 8px 8px 0;
  color: var(--blockquote-text);
  transition: background var(--t-med), border-color var(--t-med);
}
.lesson-body blockquote p { margin: 4px 0; font-size: 14px; }

/* Inline code */
.lesson-body :not(pre) > code {
  font-family: ui-monospace, SFMono-Regular, Menlo, "Courier New", monospace;
  font-size: 12.5px;
  background: var(--code-inline-bg);
  border: 1px solid var(--body-border);
  padding: 1px 5px;
  border-radius: 4px;
  color: var(--code-inline-text);
  word-break: break-word;
  transition: background var(--t-med);
}
/* The source HTML uses .language-markdown for inline code spans */
.lesson-body .language-markdown {
  font-family: ui-monospace, SFMono-Regular, Menlo, "Courier New", monospace;
  font-size: 12.5px;
  background: var(--code-inline-bg);
  border: 1px solid var(--body-border);
  padding: 1px 5px;
  border-radius: 4px;
  color: var(--code-inline-text);
}

/* Block code */
.lesson-body pre {
  background: var(--code-bg) !important;
  border: 1px solid var(--body-border) !important;
  border-radius: 8px !important;
  padding: 14px 16px !important;
  overflow-x: auto;
  margin: 12px 0 18px;
  tab-size: 2;
  transition: background var(--t-med);
}
.lesson-body pre code {
  font-family: ui-monospace, SFMono-Regular, Menlo, "Courier New", monospace;
  font-size: 13px !important;
  line-height: 1.65;
  background: transparent !important;
  border: 0 !important;
  padding: 0 !important;
  color: var(--code-text);
  white-space: pre;
}

/* Images */
.lesson-body img {
  max-width: 100%;
  height: auto;
  border-radius: 8px;
  margin: 14px 0;
  display: block;
  box-shadow: var(--shadow-sm);
  transition: transform var(--t-med), box-shadow var(--t-med);
}
.lesson-body img:hover {
  transform: scale(1.01);
  box-shadow: var(--shadow-md);
}

/* Iframes / YouTube */
.lesson-body iframe {
  width: 100%; aspect-ratio: 16 / 9;
  border: 0; border-radius: 8px;
  margin: 10px 0; display: block;
}
.lesson-body .video-container {
  margin: 14px 0 22px;
  border-radius: 8px;
  overflow: hidden;
}
.lesson-body .video-container iframe {
  border-radius: 0; margin: 0;
}

/* Tables */
.lesson-body table {
  width: 100%; border-collapse: collapse;
  margin: 16px 0; font-size: 14px;
  border-radius: 8px; overflow: hidden;
  box-shadow: var(--shadow-xs);
}
.lesson-body th, .lesson-body td {
  border: 1px solid var(--body-border);
  padding: 9px 14px; text-align: left;
}
.lesson-body th {
  background: var(--code-bg);
  font-weight: 600; font-size: 13px;
}
.lesson-body tr:hover td { background: rgba(99,102,241,0.03); }

/* KaTeX */
.lesson-body .katex { font-size: 1em; }
.lesson-body .katex-display { overflow-x: auto; margin: 14px 0; padding: 4px 0; }

/* ============================================================
   ANGULAR CUSTOM ELEMENTS
   ============================================================ */
.lesson-body app-code-tabs,
.lesson-body app-code { display: block; }
.lesson-body fa-icon {
  display: inline-flex; align-items: center; justify-content: center; line-height: 1;
}
.lesson-body fa-icon svg { width: 1em; height: 1em; vertical-align: middle; }

/* my-div wrapper — each lesson chunk starts with this */
.lesson-body .my-div { display: contents; }

/* ============================================================
   CODE TABS
   ============================================================ */
.lesson-body .code-solution-tabs-container {
  border: 1px solid var(--body-border);
  border-radius: 10px;
  overflow: hidden;
  background: var(--body-bg);
  margin: 16px 0 22px;
  box-shadow: var(--shadow-xs);
  transition: box-shadow var(--t-med), border-color var(--t-med);
}
.lesson-body .code-solution-tabs-container:hover { box-shadow: var(--shadow-sm); }

/* Tab header row */
.lesson-body .tabs-header {
  display: flex; align-items: center; justify-content: space-between;
  border-bottom: 1px solid var(--body-border);
  background: var(--tab-header-bg);
  padding: 0 8px 0 0;
  min-height: 42px;
  transition: background var(--t-med), border-color var(--t-med);
}

/* Tab list */
.lesson-body .tabs-list {
  list-style: none;
  display: flex;
  padding: 0; margin: 0;
  overflow-x: auto;
  scrollbar-width: none;
}
.lesson-body .tabs-list::-webkit-scrollbar { display: none; }
.lesson-body .tabs-list-item { display: flex; align-items: stretch; }

/* Tab buttons */
.lesson-body .tab-button {
  display: inline-flex; align-items: center;
  padding: 0 14px;
  height: 42px;
  font-size: 13px; font-weight: 500;
  color: var(--body-muted);
  cursor: pointer;
  border-bottom: 2px solid transparent;
  user-select: none; white-space: nowrap;
  text-decoration: none;
  transition: color var(--t-fast), border-color var(--t-fast);
}
.lesson-body .tab-button:hover { color: var(--body-text); text-decoration: none; }

/* Active tab */
.lesson-body .tabs-list-item.my-active-tab .tab-button,
.lesson-body .tabs-list-item.my-active-code-tab .tab-button {
  color: var(--body-text);
  border-bottom-color: var(--indigo);
  font-weight: 600;
}

/* Fullscreen / header action button */
.lesson-body .header-actions {
  display: flex; align-items: center;
  padding: 0 4px; flex-shrink: 0;
}
.lesson-body .header-actions .fullscreen-btn {
  background: transparent; border: 0;
  color: var(--body-muted); cursor: pointer;
  padding: 5px; border-radius: 5px;
  display: inline-flex; align-items: center; justify-content: center;
  transition: color var(--t-fast), background var(--t-fast);
}
.lesson-body .header-actions .fullscreen-btn:hover {
  color: var(--body-text); background: var(--code-inline-bg);
}
.lesson-body .header-actions .fullscreen-btn svg { width: 13px; height: 13px; }

/* Tab panels */
.lesson-body .code-tabs-content > .code-tab-panel { display: none; }
.lesson-body .code-tabs-content > .code-tab-panel.active { display: block; }
.lesson-body .code-tabs-content > .code-tab-panel.hidden { display: none; }

/* ============================================================
   CODE BLOCKS INSIDE TABS (app-code)
   ============================================================ */
.lesson-body .outer-container {
  position: relative;
  background: var(--code-bg);
  border-top: 1px solid var(--body-border);
  transition: background var(--t-med);
}

/* Copy button */
.lesson-body .code-actions {
  position: relative; height: 0; overflow: visible;
}
.lesson-body .code-actions .copy-btn,
.lesson-body .code-actions .code-action-btn {
  position: absolute;
  top: 8px; right: 10px; z-index: 5;
  background: var(--code-bg);
  border: 1px solid var(--body-border);
  border-radius: 5px;
  color: var(--body-muted);
  cursor: pointer;
  padding: 3px 7px;
  font-size: 11px;
  display: inline-flex; align-items: center; gap: 4px;
  opacity: 0;
  transition: opacity var(--t-fast), color var(--t-fast), background var(--t-fast);
}
.lesson-body .outer-container:hover .copy-btn,
.lesson-body .outer-container:hover .code-action-btn { opacity: 1; }
.lesson-body .code-actions .copy-btn:hover,
.lesson-body .code-actions .code-action-btn:hover {
  opacity: 1; color: var(--body-text);
  background: var(--code-inline-bg);
}
.lesson-body .code-actions .copy-btn svg { width: 12px; height: 12px; }

/* Pre/code inside app-code — outer-container is the visual box */
.lesson-body .outer-container pre {
  background: transparent !important;
  border: 0 !important;
  border-radius: 0 !important;
  margin: 0 !important;
  padding: 14px 16px !important;
}
.lesson-body .outer-container pre code {
  background: transparent !important;
  border: 0 !important; padding: 0 !important;
  font-size: 13px !important;
  line-height: 1.65;
  color: var(--code-text);
}

/* ============================================================
   TABLE OF CONTENTS (right rail)
   ============================================================ */
.toc {
  position: sticky;
  top: 56px;
  align-self: start;
  height: calc(100vh - 56px);
  overflow-y: auto;
  padding: 22px 18px 40px;
  background: var(--bg);
  border-left: 1px solid var(--border);
  font-size: 13px;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
  transition: background var(--t-med), border-color var(--t-med);
}
.toc h3 {
  margin: 0 0 10px;
  font-size: 11px; font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase; letter-spacing: 0.08em;
}
.toc ul { list-style: none; display: flex; flex-direction: column; gap: 2px; }
.toc a {
  display: block;
  color: var(--text-muted);
  border-left: 2px solid transparent;
  padding: 4px 0 4px 10px;
  margin-left: -2px;
  border-radius: 0 4px 4px 0;
  line-height: 1.4;
  transition: color var(--t-fast), border-color var(--t-fast), background var(--t-fast);
}
.toc a:hover { color: var(--text); background: var(--pill-bg); text-decoration: none; }
.toc a.h2 { font-weight: 600; color: var(--link); }
.toc a.h3 { padding-left: 22px; font-size: 12px; }
.toc a.active {
  border-left-color: var(--link);
  color: var(--link);
  background: rgba(37,99,235,0.06);
}

/* ============================================================
   RESPONSIVE
   ============================================================ */
@media (max-width: 1100px) {
  .content { grid-template-columns: minmax(0, 1fr); }
  .toc { display: none; }
}

@media (max-width: 820px) {
  :root { --sidebar-w: 280px; }
  .layout { grid-template-columns: 1fr; }

  /* Overlay sidebar on mobile */
  .sidebar {
    position: fixed;
    top: 56px; left: 0;
    height: calc(100vh - 56px);
    z-index: 40;
    transform: translateX(-100%);
    box-shadow: 4px 0 24px rgba(0,0,0,0.3);
  }
  .sidebar.open { transform: translateX(0); }

  /* Backdrop */
  .sidebar-backdrop {
    display: none;
    position: fixed; inset: 56px 0 0;
    background: rgba(0,0,0,0.45);
    z-index: 39;
    backdrop-filter: blur(2px);
    animation: fadeIn 0.2s ease both;
  }
  .sidebar-backdrop.visible { display: block; }

  .sidebar-toggle { display: inline-flex; }
  .content { grid-template-columns: 1fr; }
  .content-inner { padding: 16px 16px 60px; }
  .lesson-body { padding: 20px 16px 28px; }
}

/* ============================================================
   TOPNAV BUTTON (Courses)
   ============================================================ */
.topnav-btn {
  padding: 6px 12px;
  border-radius: 7px;
  border: 0;
  background: transparent;
  color: var(--text-muted);
  font-weight: 500;
  font-size: 13.5px;
  cursor: pointer;
  font-family: inherit;
  transition: background var(--t-fast), color var(--t-fast);
}
.topnav-btn:hover { background: var(--pill-bg); color: var(--text); }
.topnav-btn.active { background: var(--pill-bg); color: var(--text); }

/* ============================================================
   COURSES OVERLAY
   ============================================================ */
@keyframes overlayIn {
  from { opacity: 0; transform: translateY(-12px) scale(0.99); }
  to   { opacity: 1; transform: translateY(0) scale(1); }
}

.courses-overlay {
  position: fixed;
  inset: 56px 0 0 0;
  z-index: 60;
  background: var(--bg);
  overflow-y: auto;
  animation: overlayIn 0.22s cubic-bezier(0.16, 1, 0.3, 1) both;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
  border-top: 1px solid var(--border);
}
.courses-overlay[hidden] { display: none; }

.courses-overlay-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 40px 32px 80px;
}

.courses-overlay-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 36px;
}

.courses-overlay-title {
  font-size: 28px;
  font-weight: 800;
  color: var(--text);
  line-height: 1.2;
  letter-spacing: -0.02em;
}

.courses-overlay-sub {
  margin-top: 6px;
  font-size: 14px;
  color: var(--text-muted);
}

.courses-close-btn {
  width: 36px; height: 36px;
  flex-shrink: 0;
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: 9px;
  color: var(--text-muted);
  cursor: pointer;
  display: inline-flex; align-items: center; justify-content: center;
  transition: background var(--t-fast), color var(--t-fast), border-color var(--t-fast), transform var(--t-fast);
}
.courses-close-btn:hover { background: var(--pill-bg); color: var(--text); border-color: var(--indigo); }
.courses-close-btn:active { transform: scale(0.92); }

/* ---- Grid ---- */
.courses-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(310px, 1fr));
  gap: 20px;
}

/* ---- Course card ---- */
.course-card {
  position: relative;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 0;
  overflow: hidden;
  cursor: pointer;
  box-shadow: var(--shadow-sm);
  transition: transform var(--t-med), box-shadow var(--t-med), border-color var(--t-med);
  animation: fadeUp 0.3s ease both;
}
.course-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  border-color: transparent;
}
.course-card:active { transform: translateY(-1px); }

/* Top accent bar */
.course-card-accent {
  height: 4px;
  width: 100%;
}

.course-card-body {
  padding: 20px 22px 22px;
}

.course-card-icon {
  width: 40px; height: 40px;
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  margin-bottom: 14px;
  font-size: 20px;
  flex-shrink: 0;
}

.course-card-title {
  font-size: 16px;
  font-weight: 700;
  color: var(--text);
  line-height: 1.35;
  margin-bottom: 8px;
}

.course-card-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: 18px;
}

.course-tag {
  display: inline-flex; align-items: center; gap: 4px;
  padding: 3px 9px;
  border-radius: 999px;
  font-size: 11.5px;
  font-weight: 500;
  background: var(--pill-bg);
  color: var(--text-muted);
  border: 1px solid var(--border);
}
.course-tag svg { opacity: 0.7; }

.course-card-cta {
  display: inline-flex; align-items: center; gap: 6px;
  width: 100%;
  height: 36px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-size: 13px;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  padding: 0 14px;
  justify-content: center;
  transition: background var(--t-fast), border-color var(--t-fast), color var(--t-fast);
}
.course-card-cta svg { transition: transform var(--t-fast); }
.course-card:hover .course-card-cta { border-color: currentColor; }
.course-card:hover .course-card-cta svg { transform: translateX(3px); }

/* Per-course accent colors */
.course-card[data-accent="indigo"] .course-card-accent  { background: linear-gradient(90deg, #6366f1, #8b5cf6); }
.course-card[data-accent="indigo"] .course-card-cta     { color: #6366f1; background: rgba(99,102,241,0.06); border-color: rgba(99,102,241,0.25); }
.course-card[data-accent="indigo"] .course-card-icon    { background: rgba(99,102,241,0.1); }

.course-card[data-accent="blue"] .course-card-accent    { background: linear-gradient(90deg, #3b82f6, #06b6d4); }
.course-card[data-accent="blue"] .course-card-cta       { color: #3b82f6; background: rgba(59,130,246,0.06); border-color: rgba(59,130,246,0.25); }
.course-card[data-accent="blue"] .course-card-icon      { background: rgba(59,130,246,0.1); }

.course-card[data-accent="green"] .course-card-accent   { background: linear-gradient(90deg, #22c55e, #10b981); }
.course-card[data-accent="green"] .course-card-cta      { color: #16a34a; background: rgba(34,197,94,0.06); border-color: rgba(34,197,94,0.25); }
.course-card[data-accent="green"] .course-card-icon     { background: rgba(34,197,94,0.1); }

.course-card[data-accent="teal"] .course-card-accent    { background: linear-gradient(90deg, #14b8a6, #06b6d4); }
.course-card[data-accent="teal"] .course-card-cta       { color: #0d9488; background: rgba(20,184,166,0.06); border-color: rgba(20,184,166,0.25); }
.course-card[data-accent="teal"] .course-card-icon      { background: rgba(20,184,166,0.1); }

.course-card[data-accent="orange"] .course-card-accent  { background: linear-gradient(90deg, #f97316, #fbbf24); }
.course-card[data-accent="orange"] .course-card-cta     { color: #ea580c; background: rgba(249,115,22,0.06); border-color: rgba(249,115,22,0.25); }
.course-card[data-accent="orange"] .course-card-icon    { background: rgba(249,115,22,0.1); }

.course-card[data-accent="pink"] .course-card-accent    { background: linear-gradient(90deg, #ec4899, #f43f5e); }
.course-card[data-accent="pink"] .course-card-cta       { color: #db2777; background: rgba(236,72,153,0.06); border-color: rgba(236,72,153,0.25); }
.course-card[data-accent="pink"] .course-card-icon      { background: rgba(236,72,153,0.1); }

/* Dark mode adjustments */
body.theme-dark .course-card { background: var(--surface); }
body.theme-dark .course-card-cta { background: var(--pill-bg); }

@media (max-width: 480px) {
  .topbar { padding: 0 14px; }
  .topnav { display: none; }
  .course-select { max-width: 180px; }
  .lesson-body { font-size: 14.5px; border-radius: 8px; }
  .lesson-body h1 { font-size: 22px; }
  .lesson-body h2 { font-size: 18px; }
  .lesson-body pre { padding: 12px !important; font-size: 12px !important; }
  .courses-overlay-inner { padding: 24px 16px 60px; }
  .courses-overlay-title { font-size: 22px; }
  .courses-grid { grid-template-columns: 1fr; gap: 14px; }
}

@media (max-width: 820px) {
  .courses-overlay-inner { padding: 28px 20px 60px; }
}