@import url('https://fonts.googleapis.com/css2?family=Syne:wght@400;600;700;800&family=Inter:wght@300;400;500;600&family=JetBrains+Mono:wght@400;500&display=swap');

:root {
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-tertiary: #21262d;
  --bg-hover: #30363d;
  --color-border: #30363d;
  --color-text-primary: #e6edf3;
  --color-text-secondary: #8b949e;
  --color-text-muted: #6e7681;
  --accent-green: #3fb950;
  --accent-teal: #2ea89e;
  --accent-blue: #58a6ff;
  --accent-orange: #f0883e;
  --accent-purple: #bc8cff;
  --font-sans: 'Inter', sans-serif;
  --font-display: 'Syne', sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
  /* aliases for compatibility with both design systems */
  --color-background-primary: #161b22;
  --color-background-secondary: #21262d;
  --color-background-tertiary: #0d1117;
  --color-text-tertiary: #6e7681;
  --border-radius-md: 8px;
  --border-radius-lg: 12px;
  --border-radius: 8px;
  --radius: 8px;
  --radius-lg: 12px;
  --border: #30363d;
  --color-border-tertiary: #21262d;
  --color-border-secondary: #30363d;
}

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

body {
  background: var(--bg-primary);
  color: var(--color-text-primary);
  font-family: var(--font-sans);
  font-size: 14px;
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
}

/* ── Sidebar ── */
#sidebar {
  width: 280px;
  min-width: 280px;
  background: var(--bg-secondary);
  border-right: 1px solid var(--color-border);
  height: 100vh;
  overflow-y: auto;
  position: fixed;
  top: 0; left: 0;
  display: flex;
  flex-direction: column;
}

.sidebar-brand {
  padding: 18px 16px;
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  gap: 12px;
}

.brand-logo {
  width: 38px;
  height: 38px;
  background: linear-gradient(135deg, var(--accent-green), var(--accent-teal));
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
  flex-shrink: 0;
}

.sidebar-brand h1 {
  font-family: var(--font-display);
  font-size: 15px;
  font-weight: 800;
  color: var(--accent-green);
  letter-spacing: -0.3px;
}

.sidebar-brand p {
  font-size: 11px;
  color: var(--color-text-muted);
  margin-top: 1px;
}

.overall-progress {
  padding: 12px 16px;
  border-bottom: 1px solid var(--color-border);
}

.progress-label {
  display: flex;
  justify-content: space-between;
  font-size: 11px;
  color: var(--color-text-muted);
  margin-bottom: 6px;
}

.progress-bar {
  height: 4px;
  background: var(--bg-tertiary);
  border-radius: 99px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent-green), var(--accent-teal));
  border-radius: 99px;
  transition: width 0.5s ease;
}

#chapter-nav { overflow-y: auto; flex: 1; padding: 8px 0; }

.chapter-group { padding: 4px 0; }

.chapter-header {
  padding: 7px 16px;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.7px;
  color: var(--color-text-muted);
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 8px;
  transition: color 0.15s;
}

.chapter-header:hover, .chapter-header.active-chapter { color: var(--color-text-secondary); }
.chapter-header .ch-title { flex: 1; line-height: 1.3; }
.chapter-header .ch-status { font-size: 10px; flex-shrink: 0; }

.lesson-list { display: none; }
.lesson-list.open { display: block; }

.lesson-item {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  padding: 6px 16px 6px 24px;
  font-size: 12.5px;
  color: var(--color-text-secondary);
  cursor: pointer;
  border-left: 2px solid transparent;
  transition: all 0.15s;
  line-height: 1.4;
}

.lesson-item:hover { background: var(--bg-tertiary); color: var(--color-text-primary); }
.lesson-item.active { color: var(--accent-green); border-left-color: var(--accent-green); background: rgba(63,185,80,0.06); font-weight: 500; }
.lesson-item.completed { color: var(--color-text-muted); }
.lesson-item .li-icon { font-size: 10px; min-width: 14px; margin-top: 2px; }
.lesson-item .li-title { flex: 1; }

/* ── Main ── */
#main {
  margin-left: 280px;
  flex: 1;
  min-height: 100vh;
}

#lesson-view {
  max-width: 840px;
  margin: 0 auto;
  padding: 40px 48px 80px;
}

.lesson-wrapper { display: flex; flex-direction: column; gap: 0; }

/* ── Lesson content classes (original system ch1-11) ── */
.lesson-tag {
  display: inline-block;
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  padding: 3px 12px;
  border-radius: 99px;
  margin-bottom: 14px;
}
.tag-lesson, .lesson-tag:not(.tag-quiz):not(.tag-lab) {
  background: rgba(63,185,80,0.12);
  color: var(--accent-green);
  border: 1px solid rgba(63,185,80,0.2);
}
.tag-quiz { background: rgba(88,166,255,0.12); color: var(--accent-blue); border: 1px solid rgba(88,166,255,0.2); }
.tag-lab { background: rgba(46,168,158,0.12); color: var(--accent-teal); border: 1px solid rgba(46,168,158,0.2); }

.lesson-title {
  font-family: var(--font-display);
  font-size: 28px;
  font-weight: 700;
  color: var(--color-text-primary);
  line-height: 1.2;
  margin-bottom: 10px;
  letter-spacing: -0.5px;
}

.lesson-meta {
  display: flex;
  gap: 16px;
  margin-bottom: 28px;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--color-border);
  flex-wrap: wrap;
}

.lesson-meta span, .meta-item {
  font-size: 12px;
  color: var(--color-text-muted);
  display: flex;
  align-items: center;
  gap: 4px;
}

.lesson-section-title {
  font-family: var(--font-display);
  font-size: 17px;
  font-weight: 700;
  color: var(--color-text-primary);
  margin: 28px 0 10px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  gap: 8px;
}

.lesson-section-title::before {
  content: '';
  display: block;
  width: 3px;
  height: 16px;
  background: var(--accent-green);
  border-radius: 99px;
  flex-shrink: 0;
}

.lesson-text {
  color: var(--color-text-secondary);
  font-size: 14px;
  line-height: 1.8;
  margin-bottom: 14px;
}

.lesson-text code, code {
  font-family: var(--font-mono);
  font-size: 12px;
  background: var(--bg-tertiary);
  padding: 1px 6px;
  border-radius: 4px;
  color: var(--accent-teal);
  border: 1px solid var(--color-border);
}

/* ── Code blocks ── */
.code-block {
  background: var(--bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  margin: 18px 0;
}

.code-block-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 14px;
  background: var(--bg-tertiary);
  border-bottom: 1px solid var(--color-border);
}

.code-filename {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--color-text-muted);
  display: flex;
  align-items: center;
  gap: 6px;
}

.code-filename::before { content: '●'; color: var(--accent-orange); font-size: 9px; }

.code-lang { font-size: 10px; color: var(--accent-green); text-transform: uppercase; letter-spacing: 0.5px; }

.copy-btn {
  font-size: 11px;
  color: var(--color-text-muted);
  background: none;
  border: none;
  cursor: pointer;
  font-family: var(--font-sans);
  padding: 3px 8px;
  border-radius: 4px;
  transition: all 0.15s;
}
.copy-btn:hover { background: var(--bg-hover); color: var(--color-text-secondary); }

.code-block pre {
  padding: 18px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 13px;
  line-height: 1.75;
  color: var(--color-text-primary);
}

/* Syntax highlight classes */
.kw { color: #ff7b72; }
.fn { color: #d2a8ff; }
.st { color: #a5d6ff; }
.cm { color: #8b949e; font-style: italic; }
.nm { color: #f2cc60; }
.op { color: #8b949e; }

/* ── Lab box ── */
.lab-box {
  border: 1px solid rgba(46,168,158,0.3);
  border-left: 4px solid var(--accent-teal);
  background: rgba(46,168,158,0.05);
  border-radius: var(--radius-lg);
  padding: 18px 20px;
  margin: 20px 0;
}

.lab-box-title {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--accent-teal);
  margin-bottom: 14px;
  display: flex;
  align-items: center;
  gap: 6px;
}

.lab-box ol {
  padding-left: 18px;
  color: var(--color-text-secondary);
  font-size: 13.5px;
  line-height: 1.9;
}

.lab-box ol li { margin-bottom: 5px; }
.lab-box ol li::marker { color: var(--accent-teal); font-weight: 600; }

/* ── Lab steps (original system) ── */
.lab-steps { display: flex; flex-direction: column; gap: 10px; margin-top: 4px; }
.lab-step { display: flex; gap: 12px; align-items: flex-start; font-size: 13px; color: var(--color-text-secondary); line-height: 1.6; }
.step-num {
  min-width: 22px; height: 22px;
  border-radius: 50%;
  background: rgba(46,168,158,0.15);
  border: 1px solid rgba(46,168,158,0.3);
  color: var(--accent-teal);
  font-size: 11px; font-weight: 600;
  display: flex; align-items: center; justify-content: center;
  font-family: var(--font-mono);
  flex-shrink: 0; margin-top: 1px;
}

/* ── Tip / Warn boxes ── */
.tip-box {
  border: 1px solid rgba(88,166,255,0.25);
  border-left: 4px solid var(--accent-blue);
  background: rgba(88,166,255,0.05);
  border-radius: var(--radius);
  padding: 14px 18px;
  margin: 16px 0;
  color: var(--color-text-secondary);
  font-size: 13px;
  line-height: 1.7;
}

.warn-box {
  border: 1px solid rgba(240,136,62,0.25);
  border-left: 4px solid var(--accent-orange);
  background: rgba(240,136,62,0.05);
  border-radius: var(--radius);
  padding: 14px 18px;
  margin: 16px 0;
  color: var(--color-text-secondary);
  font-size: 13px;
  line-height: 1.7;
}

/* ── Stack diagram ── */
.stack-diagram { display: flex; flex-direction: column; gap: 3px; margin: 18px 0; }
.stack-layer {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 11px 16px;
  border-radius: 8px;
  font-size: 13px;
  border: 1px solid var(--color-border);
}
.stack-layer.l1 { background: rgba(188,140,255,0.07); border-color: rgba(188,140,255,0.2); }
.stack-layer.l2 { background: rgba(88,166,255,0.07); border-color: rgba(88,166,255,0.2); }
.stack-layer.l3 { background: rgba(46,168,158,0.07); border-color: rgba(46,168,158,0.2); }
.stack-layer.l4 { background: rgba(63,185,80,0.07); border-color: rgba(63,185,80,0.2); }
.stack-num {
  font-family: var(--font-mono);
  font-size: 11px; font-weight: 700;
  min-width: 28px; height: 28px;
  border-radius: 6px;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0;
}
.l1 .stack-num { background: rgba(188,140,255,0.2); color: var(--accent-purple); }
.l2 .stack-num { background: rgba(88,166,255,0.2); color: var(--accent-blue); }
.l3 .stack-num { background: rgba(46,168,158,0.2); color: var(--accent-teal); }
.l4 .stack-num { background: rgba(63,185,80,0.2); color: var(--accent-green); }
.stack-info { flex: 1; line-height: 1.5; }
.stack-name { font-weight: 500; color: var(--color-text-primary); }
.stack-desc { font-size: 12px; color: var(--color-text-secondary); margin-top: 2px; }

/* ── Quiz ── */
.quiz-container { display: flex; flex-direction: column; gap: 24px; }

.quiz-question {
  background: var(--bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 20px;
}

.quiz-q-text {
  font-weight: 600;
  color: var(--color-text-primary);
  margin-bottom: 14px;
  line-height: 1.5;
  font-size: 14px;
}

.quiz-options { display: flex; flex-direction: column; gap: 8px; }

.quiz-option {
  display: flex; align-items: flex-start; gap: 10px;
  padding: 10px 14px;
  background: var(--bg-tertiary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  cursor: pointer; transition: all 0.15s;
  font-size: 13px; color: var(--color-text-secondary);
  text-align: left; width: 100%;
  font-family: var(--font-sans);
}

.quiz-option:hover:not(:disabled) { border-color: var(--accent-blue); color: var(--color-text-primary); }
.quiz-option.correct { border-color: var(--accent-green); background: rgba(63,185,80,0.08); color: var(--accent-green); }
.quiz-option.wrong { border-color: #f85149; background: rgba(248,81,73,0.08); color: #f85149; }
.quiz-option:disabled { cursor: default; }
.opt-letter { font-weight: 700; min-width: 16px; flex-shrink: 0; }

/* Also support original quiz style (quiz-opt / quiz-dot) */
.quiz-opt {
  display: flex; align-items: center; gap: 8px;
  padding: 8px 12px;
  border-radius: 8px;
  border: 1px solid var(--color-border);
  font-size: 13px; color: var(--color-text-secondary);
  cursor: pointer; transition: all 0.15s;
  background: var(--bg-tertiary);
  font-family: var(--font-sans); width: 100%;
}
.quiz-opt:hover { border-color: var(--accent-green); color: var(--color-text-primary); }
.quiz-opt.correct { border-color: var(--accent-green); background: rgba(63,185,80,0.08); color: var(--accent-green); }
.quiz-opt.wrong { border-color: #f85149; background: rgba(248,81,73,0.08); color: #f85149; }
.quiz-dot { width: 14px; height: 14px; border-radius: 50%; border: 1.5px solid var(--color-border); flex-shrink: 0; }
.quiz-opt.correct .quiz-dot { border-color: var(--accent-green); background: var(--accent-green); }
.quiz-opt.wrong .quiz-dot { border-color: #f85149; background: #f85149; }
.quiz-feedback { margin-top: 8px; font-size: 11px; padding: 6px 10px; border-radius: 6px; }
.correct-fb { background: rgba(63,185,80,0.1); color: var(--accent-green); }
.wrong-fb { background: rgba(248,81,73,0.1); color: #f85149; }

.quiz-explanation { margin-top: 12px; font-size: 12px; color: var(--color-text-muted); padding: 8px 12px; background: var(--bg-tertiary); border-radius: 6px; }

.quiz-score-bar {
  text-align: right;
  font-size: 12px;
  color: var(--accent-green);
  margin-top: 8px;
  font-family: var(--font-mono);
}

/* ── Navigation buttons ── */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--color-border);
}

.nav-btn {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 10px 20px;
  background: var(--bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  color: var(--color-text-secondary);
  font-size: 13px; font-weight: 500;
  cursor: pointer;
  font-family: var(--font-sans);
  transition: all 0.15s;
}

.nav-btn:hover { border-color: var(--accent-green); color: var(--color-text-primary); }
.nav-btn.primary { background: var(--accent-green); color: #000; border-color: var(--accent-green); font-weight: 600; }
.nav-btn.primary:hover { background: #56d364; }

/* ── Welcome screen ── */
.welcome-screen {
  display: flex; flex-direction: column;
  align-items: center; justify-content: center;
  min-height: 60vh; text-align: center; padding: 40px;
}

.welcome-screen h2 {
  font-family: var(--font-display);
  font-size: 40px; font-weight: 800;
  background: linear-gradient(135deg, var(--accent-green), var(--accent-teal));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  margin-bottom: 14px;
}

.welcome-screen p { color: var(--color-text-secondary); max-width: 480px; line-height: 1.7; font-size: 15px; }

/* ── Lists ── */
ul, ol {
  color: var(--color-text-secondary);
  font-size: 14px;
  line-height: 1.9;
  padding-left: 22px;
  margin-bottom: 16px;
}

li { margin-bottom: 4px; }

strong { color: var(--color-text-primary); font-weight: 600; }
em { color: var(--color-text-secondary); font-style: italic; }

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 5px; height: 5px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--bg-hover); border-radius: 99px; }

/* ── Responsive ── */
@media (max-width: 768px) {
  #sidebar { width: 100%; height: auto; position: relative; }
  #main { margin-left: 0; }
  #lesson-view { padding: 24px 20px 60px; }
  body { flex-direction: column; }
}