:root {
  --bg: #07090f;
  --bg2: #0b0f1a;
  --bg3: #0f1525;
  --panel: #111827;
  --panel2: #141e2e;
  --border: #1c2a3a;
  --border-hi: #243448;
  --cyan: #22d3ee;
  --cyan-dim: rgba(34,211,238,0.1);
  --cyan-glow: rgba(34,211,238,0.3);
  --cyan-dark: #0891b2;
  --blue: #60a5fa;
  --purple: #a78bfa;
  --green: #4ade80;
  --orange: #fb923c;
  --pink: #f472b6;
  --muted: #3d5468;
  --soft: #6b8ca8;
  --text: #c8dce8;
  --white: #e8f4fc;
  --sidebar-w: 270px;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Inter', sans-serif;
  background: var(--bg);
  color: var(--text);
  display: flex;
  min-height: 100vh;
  font-size: 15px;
  line-height: 1.6;
}

/* ── SIDEBAR ── */
#sidebar {
  width: var(--sidebar-w);
  background: var(--bg2);
  border-right: 1px solid var(--border);
  position: fixed;
  top: 0; left: 0; bottom: 0;
  overflow-y: auto;
  z-index: 100;
  display: flex;
  flex-direction: column;
}

.brand {
  padding: 20px;
  border-bottom: 1px solid var(--border);
}

.brand-mark {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 6px;
}

.brand-icon {
  width: 30px; height: 30px;
  background: var(--cyan-dim);
  border: 1px solid rgba(34,211,238,0.3);
  border-radius: 7px;
  display: flex; align-items: center; justify-content: center;
  font-size: 14px;
}

.brand-title {
  font-family: 'JetBrains Mono', monospace;
  font-size: 14px;
  font-weight: 700;
  color: var(--cyan);
}

.brand-sub {
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 1px;
}

.prog-wrap {
  padding: 12px 20px;
  border-bottom: 1px solid var(--border);
}

.prog-meta {
  display: flex;
  justify-content: space-between;
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  color: var(--muted);
  margin-bottom: 6px;
}

.prog-track {
  height: 3px;
  background: var(--bg3);
  border-radius: 2px;
}

.prog-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--cyan-dark), var(--cyan));
  border-radius: 2px;
  transition: width 0.4s ease;
  width: 0%;
}

.nav-section { padding: 10px 0; }

.nav-group-label {
  padding: 6px 20px 4px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 1px;
}

.nav-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 7px 20px;
  cursor: pointer;
  border-left: 3px solid transparent;
  font-size: 12.5px;
  color: var(--soft);
  transition: all 0.15s;
}

.nav-item:hover { background: var(--bg3); color: var(--white); }
.nav-item.active {
  background: rgba(34,211,238,0.06);
  border-left-color: var(--cyan);
  color: var(--cyan);
}
.nav-item.done { color: var(--soft); }
.nav-item.done .nav-chk { color: var(--cyan); }

.nav-n {
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  color: var(--muted);
  min-width: 18px;
}
.nav-chk { font-size: 11px; min-width: 18px; text-align: center; }

/* ── MAIN ── */
#main {
  margin-left: var(--sidebar-w);
  flex: 1;
  min-height: 100vh;
}

.topbar {
  background: var(--bg2);
  border-bottom: 1px solid var(--border);
  padding: 10px 40px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 50;
}

.breadcrumb {
  font-family: 'JetBrains Mono', monospace;
  font-size: 11.5px;
  color: var(--muted);
}
.breadcrumb span { color: var(--cyan); }

.topbar-btns { display: flex; gap: 8px; }

.btn {
  padding: 5px 13px;
  border-radius: 6px;
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  border: 1px solid var(--border-hi);
  background: var(--panel);
  color: var(--soft);
  transition: all 0.15s;
  font-family: 'Inter', sans-serif;
}
.btn:hover { color: var(--white); border-color: var(--soft); }
.btn-primary {
  background: var(--cyan-dark);
  border-color: var(--cyan-dark);
  color: #fff;
}
.btn-primary:hover { background: var(--cyan); border-color: var(--cyan); color: #07090f; }

/* ── LESSON WRAP ── */
.lesson-wrap {
  max-width: 860px;
  margin: 0 auto;
  padding: 48px 40px 80px;
}

.lesson-eyebrow {
  font-family: 'JetBrains Mono', monospace;
  font-size: 11px;
  color: var(--cyan);
  text-transform: uppercase;
  letter-spacing: 1.5px;
  margin-bottom: 10px;
}

.lesson-title {
  font-family: 'JetBrains Mono', monospace;
  font-size: clamp(24px, 4vw, 34px);
  font-weight: 700;
  color: var(--white);
  line-height: 1.15;
  letter-spacing: -0.5px;
  margin-bottom: 16px;
}

.lesson-lead {
  font-size: 16px;
  color: var(--soft);
  line-height: 1.75;
  margin-bottom: 36px;
  padding-bottom: 28px;
  border-bottom: 1px solid var(--border);
}

h2 {
  font-family: 'JetBrains Mono', monospace;
  font-size: 18px;
  font-weight: 600;
  color: var(--white);
  margin: 32px 0 12px;
  letter-spacing: -0.3px;
}

h3 {
  font-size: 14px;
  font-weight: 600;
  color: var(--white);
  margin: 22px 0 8px;
}

p { margin-bottom: 14px; color: var(--soft); }

/* ── PIPELINE DIAGRAM (signature element) ── */
.pipeline {
  background: var(--bg3);
  border: 1px solid var(--border-hi);
  border-radius: 10px;
  padding: 24px 20px;
  margin: 24px 0;
  overflow-x: auto;
}

.pipeline-label {
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 16px;
}

.pipe-row {
  display: flex;
  align-items: stretch;
  gap: 0;
  min-width: max-content;
}

.pipe-node {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
}

.pipe-box {
  background: var(--panel2);
  border: 1px solid var(--border-hi);
  border-radius: 7px;
  padding: 8px 14px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 12px;
  white-space: nowrap;
  position: relative;
}

.pipe-box.source { border-color: rgba(96,165,250,0.5); color: var(--blue); }
.pipe-box.intermediate { border-color: rgba(34,211,238,0.4); color: var(--cyan); }
.pipe-box.terminal-op { border-color: rgba(74,222,128,0.5); color: var(--green); }
.pipe-box.data { border-color: var(--border); color: var(--muted); font-size: 11px; }

.pipe-tag {
  font-size: 9px;
  color: var(--muted);
  font-family: 'JetBrains Mono', monospace;
  text-transform: uppercase;
}

.pipe-arrow {
  display: flex;
  align-items: center;
  padding: 0 4px;
  padding-top: 8px;
}

.pipe-arrow-line {
  width: 28px;
  height: 2px;
  background: linear-gradient(90deg, var(--border-hi), var(--cyan-dark));
  position: relative;
}

.pipe-arrow-line::after {
  content: '';
  position: absolute;
  right: -4px;
  top: -3px;
  border: 4px solid transparent;
  border-left-color: var(--cyan-dark);
}

/* ── CODE BLOCKS ── */
.code-block {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  margin: 18px 0;
  overflow: hidden;
}

.code-head {
  background: var(--bg3);
  padding: 7px 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--border);
}

.code-fn { font-family: 'JetBrains Mono', monospace; font-size: 11px; color: var(--soft); }
.code-tag {
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  color: var(--muted);
  background: var(--bg);
  border: 1px solid var(--border);
  padding: 2px 7px;
  border-radius: 4px;
}

pre {
  padding: 18px 20px;
  overflow-x: auto;
  font-family: 'JetBrains Mono', monospace;
  font-size: 12.5px;
  line-height: 1.8;
  color: var(--white);
}

.kw { color: var(--purple); }
.ann { color: var(--orange); }
.str { color: var(--green); }
.num { color: var(--blue); }
.cm { color: var(--muted); font-style: italic; }
.cls { color: var(--blue); }
.fn { color: #c084fc; }
.op { color: var(--cyan); }
.ret { color: var(--orange); }
.lam { color: var(--cyan); }

/* ── CALLOUTS ── */
.callout {
  border-radius: 8px;
  padding: 14px 18px;
  margin: 18px 0;
  border-left: 3px solid;
  display: flex;
  gap: 12px;
}
.callout-info { background: rgba(96,165,250,0.07); border-color: var(--blue); }
.callout-warn { background: rgba(251,146,60,0.07); border-color: var(--orange); }
.callout-tip  { background: rgba(34,211,238,0.07); border-color: var(--cyan); }
.callout-key  { background: rgba(167,139,250,0.07); border-color: var(--purple); }

.callout-icon { font-size: 15px; line-height: 1.6; }
.callout-body { flex: 1; }
.callout-title { font-weight: 600; font-size: 13px; margin-bottom: 3px; color: var(--white); }
.callout p { margin: 0; font-size: 13px; }

/* ── CONCEPT GRID ── */
.cg {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
  margin: 18px 0;
}

.cc {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 14px 16px;
  transition: border-color 0.15s;
}
.cc:hover { border-color: var(--cyan); }
.cc-icon { font-size: 18px; margin-bottom: 6px; }
.cc-title { font-weight: 600; font-size: 12.5px; margin-bottom: 4px; color: var(--white); }
.cc p { font-size: 12px; margin: 0; }

/* ── STREAM COMPARISON TABLE ── */
.compare-table {
  width: 100%;
  border-collapse: collapse;
  margin: 18px 0;
  font-size: 13px;
}
.compare-table th {
  background: var(--bg3);
  padding: 10px 14px;
  text-align: left;
  font-family: 'JetBrains Mono', monospace;
  font-size: 11px;
  color: var(--cyan);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  border-bottom: 1px solid var(--border-hi);
}
.compare-table td {
  padding: 10px 14px;
  border-bottom: 1px solid var(--border);
  color: var(--soft);
  vertical-align: top;
}
.compare-table tr:hover td { background: rgba(34,211,238,0.03); }
.compare-table td:first-child {
  font-family: 'JetBrains Mono', monospace;
  font-size: 12px;
  color: var(--cyan);
  white-space: nowrap;
}

/* ── QUIZ ── */
.quiz-box {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 24px;
  margin: 32px 0;
}

.quiz-hdr {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 18px;
}

.quiz-badge {
  background: var(--cyan-dark);
  color: #fff;
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  font-weight: 700;
  padding: 3px 8px;
  border-radius: 4px;
  text-transform: uppercase;
}

.quiz-title { font-weight: 600; font-size: 14px; color: var(--white); }

.quiz-q {
  margin-bottom: 20px;
  padding-bottom: 20px;
  border-bottom: 1px solid var(--border);
}
.quiz-q:last-child { margin-bottom: 0; padding-bottom: 0; border-bottom: none; }

.quiz-question { font-size: 13.5px; font-weight: 500; color: var(--white); margin-bottom: 10px; }

.quiz-opts { display: flex; flex-direction: column; gap: 7px; }

.qopt {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 9px 13px;
  border: 1px solid var(--border);
  border-radius: 6px;
  cursor: pointer;
  font-size: 13px;
  color: var(--soft);
  background: var(--bg2);
  transition: all 0.15s;
}
.qopt:hover { border-color: var(--cyan); color: var(--white); background: var(--cyan-dim); }
.qopt.correct { border-color: var(--cyan); background: rgba(34,211,238,0.1); color: var(--cyan); }
.qopt.wrong { border-color: var(--orange); background: rgba(251,146,60,0.08); color: var(--orange); }
.qopt.disabled { pointer-events: none; }

.qdot { width: 15px; height: 15px; border-radius: 50%; border: 2px solid var(--border-hi); flex-shrink: 0; margin-top: 2px; }
.qopt.correct .qdot { background: var(--cyan); border-color: var(--cyan); }
.qopt.wrong .qdot { background: var(--orange); border-color: var(--orange); }

.qexp {
  display: none;
  margin-top: 8px;
  padding: 10px 13px;
  background: rgba(34,211,238,0.05);
  border-left: 3px solid var(--cyan);
  border-radius: 5px;
  font-size: 12.5px;
  color: var(--soft);
}

/* ── CHALLENGE ── */
.challenge {
  background: linear-gradient(135deg, rgba(34,211,238,0.05), rgba(8,145,178,0.03));
  border: 1px solid rgba(34,211,238,0.25);
  border-radius: 10px;
  padding: 22px;
  margin: 28px 0;
}
.challenge-hdr { display: flex; align-items: center; gap: 10px; margin-bottom: 12px; }
.challenge-icon { font-size: 18px; }
.challenge-title { font-weight: 700; font-size: 14px; color: var(--cyan); }
.challenge p { font-size: 13px; color: var(--soft); }
.challenge ul { margin: 8px 0 0 16px; }
.challenge li { font-size: 13px; color: var(--soft); margin-bottom: 5px; }

/* ── LESSON NAV ── */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 48px;
  padding-top: 22px;
  border-top: 1px solid var(--border);
}

.lnav-btn {
  display: flex;
  flex-direction: column;
  gap: 3px;
  cursor: pointer;
  padding: 10px 14px;
  border: 1px solid var(--border);
  border-radius: 7px;
  background: var(--panel);
  text-decoration: none;
  transition: border-color 0.15s;
  max-width: 210px;
}
.lnav-btn:hover { border-color: var(--cyan); }
.lnav-label { font-size: 10px; color: var(--muted); font-family: 'JetBrains Mono', monospace; text-transform: uppercase; }
.lnav-title { font-size: 12.5px; color: var(--white); font-weight: 500; }

/* ── PANELS ── */
.lesson-panel { display: none; }
.lesson-panel.active { display: block; }

    .main { 
        width: 100% !important; 
        padding: 15px !important;
    }
    .lesson-nav { 
        flex-direction: column; 
        gap: 10px; 
    }
    button, .nav-btn, .btn { 
        min-height: 44px !important; 
        padding: 12px !important;
    }

/* Mobile Responsive Overrides */
@media (max-width: 768px) {
    .shell, .layout { flex-direction: column !important; }
    .sidebar { width: 100% !important; position: static !important; margin-bottom: 20px; }
    .main { width: 100% !important; padding: 15px !important; }
    .lesson-nav { flex-direction: column; gap: 10px; }
    button, .nav-btn, .btn { min-height: 44px !important; padding: 12px !important; }
    .cg { grid-template-columns: 1fr !important; }
}