:root {
  --bg: #070a0f;
  --surface: #0d1117;
  --surface-2: #111827;
  --card: rgba(17, 24, 39, 0.92);
  --border: rgba(148, 163, 184, 0.18);
  --text: #e5edf7;
  --muted: #9aa7bb;
  --dim: #64748b;
  --red: #e53935;
  --orange: #f97316;
  --amber: #fbbf24;
  --green: #22c55e;
  --teal: #06d6a0;
  --blue: #3b82f6;
  --purple: #a855f7;
  --danger: #fb7185;
  --ok: #4ade80;
  --warn: #facc15;
  --code: #08111c;
  --shadow: 0 24px 80px rgba(0, 0, 0, 0.42);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--text);
  background:
    radial-gradient(circle at 14% 4%, rgba(229, 57, 53, 0.18), transparent 32rem),
    radial-gradient(circle at 88% 20%, rgba(251, 191, 36, 0.12), transparent 26rem),
    linear-gradient(180deg, #070a0f 0%, #09101b 50%, #070a0f 100%);
  font-family: Inter, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  min-height: 100vh;
}
a { color: inherit; }
.back-link {
  position: fixed;
  left: 22px;
  bottom: 22px;
  z-index: 50;
  padding: 10px 16px;
  border-radius: 999px;
  text-decoration: none;
  background: rgba(13, 17, 23, 0.92);
  border: 1px solid var(--border);
  color: var(--text);
  font-weight: 900;
  font-size: 13px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(10px);
}

header {
  padding: 84px 24px 34px;
  border-bottom: 1px solid var(--border);
}
.hero {
  width: min(1180px, 100%);
  margin: 0 auto;
  display: grid;
  grid-template-columns: minmax(0, 1.08fr) minmax(320px, 0.92fr);
  gap: 32px;
  align-items: center;
}
.eyebrow {
  color: var(--teal);
  font: 800 0.78rem/1 JetBrains Mono, monospace;
  text-transform: lowercase;
  letter-spacing: 0.08em;
}
h1, h2, h3, p { margin-top: 0; }
h1 {
  margin: 16px 0 18px;
  font-size: clamp(3rem, 8vw, 6.8rem);
  line-height: 0.9;
  letter-spacing: -0.075em;
}
h1 span { color: var(--amber); text-shadow: 0 0 30px rgba(251, 191, 36, 0.22); }
.hero-sub {
  color: var(--muted);
  max-width: 720px;
  font-size: clamp(1rem, 1.6vw, 1.2rem);
  line-height: 1.7;
}
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 26px; }
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 46px;
  padding: 0 18px;
  border-radius: 14px;
  border: 1px solid var(--border);
  text-decoration: none;
  font-weight: 900;
  cursor: pointer;
  transition: transform .18s ease, border-color .18s ease, background .18s ease;
}
.btn:hover { transform: translateY(-2px); }
.btn.primary { background: var(--amber); border-color: rgba(255,255,255,.18); color: #111827; box-shadow: 0 14px 40px rgba(251, 191, 36, 0.22); }
.btn.ghost { background: rgba(255,255,255,0.04); color: var(--text); }

.parts-card {
  border: 1px solid rgba(251, 191, 36, 0.38);
  background: rgba(8, 13, 20, 0.88);
  border-radius: 22px;
  overflow: hidden;
  box-shadow: var(--shadow);
}
.parts-top {
  height: 44px;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 0 16px;
  border-bottom: 1px solid var(--border);
  background: rgba(255,255,255,0.04);
}
.parts-top span { width: 11px; height: 11px; border-radius: 50%; display: inline-block; }
.parts-top span:nth-child(1) { background: #ff5f56; }
.parts-top span:nth-child(2) { background: #ffbd2e; }
.parts-top span:nth-child(3) { background: #27c93f; }
.parts-top strong { margin-left: 6px; color: var(--muted); font: 800 0.8rem JetBrains Mono, monospace; }
.parts-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 10px; padding: 18px; }
.part { padding: 14px; border-radius: 16px; background: rgba(255,255,255,0.045); border: 1px solid var(--border); }
.part b { display:block; margin-bottom: 4px; color: #fff0b3; }
.part span { color: var(--muted); font-size: 0.85rem; line-height: 1.45; }

.progress-wrap {
  position: sticky;
  top: 0;
  z-index: 30;
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 12px 24px;
  background: rgba(7,10,15,0.88);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(14px);
}
.progress-label, .progress-pct { font: 900 0.78rem JetBrains Mono, monospace; color: var(--muted); white-space: nowrap; }
.progress-track { flex: 1; height: 9px; border-radius: 999px; background: rgba(255,255,255,0.07); overflow: hidden; border: 1px solid var(--border); }
.progress-fill { height: 100%; width: 0%; border-radius: inherit; background: linear-gradient(90deg, var(--amber), var(--teal)); transition: width .25s ease; }
.reset-btn { background: transparent; border: 1px solid var(--border); color: var(--muted); border-radius: 10px; padding: 6px 10px; font-weight: 900; cursor: pointer; }

.layout {
  width: min(1180px, calc(100% - 48px));
  margin: 34px auto 80px;
  display: grid;
  grid-template-columns: 300px minmax(0, 1fr);
  gap: 22px;
  align-items: start;
}
.sidebar {
  position: sticky;
  top: 74px;
  border: 1px solid var(--border);
  border-radius: 22px;
  background: rgba(13, 17, 23, 0.76);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.sidebar-title { padding: 18px 18px 12px; color: var(--amber); font: 900 .82rem JetBrains Mono, monospace; border-bottom: 1px solid var(--border); }
.nav-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 16px;
  border-bottom: 1px solid rgba(148, 163, 184, 0.10);
  color: var(--muted);
  font-weight: 800;
  cursor: pointer;
  transition: background .18s ease, color .18s ease;
}
.nav-item:last-child { border-bottom: 0; }
.nav-item:hover, .nav-item.active { background: rgba(251, 191, 36, 0.10); color: var(--text); }
.nav-item.done .nav-check { color: var(--ok); }
.nav-icon { width: 24px; text-align:center; }
.nav-check { margin-left: auto; font-weight: 900; }
.mobile-select-wrap { display: none; width: min(1180px, calc(100% - 48px)); margin: 22px auto 0; }
.mobile-select-wrap select { width: 100%; padding: 14px; color: var(--text); background: var(--surface); border: 1px solid var(--border); border-radius: 14px; font-weight: 900; }

.main { min-width: 0; }
.lesson { display: none; }
.lesson.active { display: block; animation: fadeUp .22s ease; }
@keyframes fadeUp { from { opacity: 0; transform: translateY(8px);} to { opacity: 1; transform: translateY(0);} }
.lesson-header {
  border: 1px solid rgba(251, 191, 36, 0.32);
  border-radius: 24px;
  background: linear-gradient(135deg, rgba(251, 191, 36, 0.12), rgba(6, 214, 160, 0.06));
  padding: 28px;
  margin-bottom: 18px;
}
.lesson-num { color: var(--teal); font: 900 0.78rem JetBrains Mono, monospace; text-transform: uppercase; letter-spacing: .08em; }
.lesson-header h2 { margin: 10px 0 10px; font-size: clamp(2rem, 5vw, 3.35rem); letter-spacing: -0.06em; }
.lesson-intro { color: var(--muted); line-height: 1.7; max-width: 820px; margin-bottom: 0; }
.card, .quiz-block, .lab-card {
  border: 1px solid var(--border);
  border-radius: 20px;
  background: var(--card);
  padding: 24px;
  margin: 18px 0;
}
.card-title { font-weight: 900; font-size: 1.18rem; margin-bottom: 12px; color: #fff4c4; }
.card p, .card li, .lab-card p, .lab-card li { color: var(--muted); line-height: 1.72; }
.card strong, .lab-card strong { color: var(--text); }
ul, ol { padding-left: 1.25rem; }
.step-list li { margin: 10px 0; }
.grid-2 { display: grid; grid-template-columns: repeat(2, 1fr); gap: 14px; }
.mini-card { border: 1px solid var(--border); border-radius: 16px; padding: 16px; background: rgba(255,255,255,0.035); }
.mini-card h4 { margin: 0 0 8px; color: var(--teal); }
.mini-card p { margin-bottom: 0; }
.callout {
  display: grid;
  grid-template-columns: 42px 1fr;
  gap: 12px;
  align-items: start;
  margin: 16px 0;
  padding: 16px;
  border-radius: 16px;
  border: 1px solid var(--border);
  background: rgba(255,255,255,0.04);
}
.callout.warn { border-color: rgba(251, 191, 36, 0.38); background: rgba(251, 191, 36, 0.08); }
.callout.danger { border-color: rgba(251, 113, 133, 0.42); background: rgba(251, 113, 133, 0.08); }
.callout.tip { border-color: rgba(6, 214, 160, 0.32); background: rgba(6, 214, 160, 0.08); }
.callout-emoji { font-size: 1.5rem; }
.callout-body { color: var(--muted); line-height: 1.65; }
.callout-body strong { display: block; color: var(--text); margin-bottom: 2px; }
.code-block, pre.code-block {
  background: var(--code);
  border: 1px solid rgba(6, 214, 160, 0.18);
  border-radius: 16px;
  padding: 18px;
  overflow-x: auto;
  color: #c9fddf;
  font: .88rem/1.65 JetBrains Mono, monospace;
  margin: 16px 0;
}
table { width: 100%; border-collapse: collapse; margin: 16px 0; overflow: hidden; border-radius: 14px; }
th, td { border: 1px solid var(--border); padding: 12px; text-align: left; color: var(--muted); vertical-align: top; }
th { color: var(--text); background: rgba(255,255,255,0.055); }
.lab-card { border-color: rgba(6, 214, 160, 0.30); background: linear-gradient(135deg, rgba(6,214,160,0.09), rgba(17,24,39,0.92)); }
.lab-card .card-title { color: #c9ffe9; }
.quiz-block { border-color: rgba(59, 130, 246, 0.28); }
.quiz-title { color: #bfdbfe; font-weight: 900; margin-bottom: 10px; }
.quiz-q { color: var(--text); font-weight: 800; margin-bottom: 12px; }
.quiz-options { display: grid; gap: 10px; }
.quiz-option {
  text-align: left;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: rgba(255,255,255,0.04);
  color: var(--text);
  padding: 13px 14px;
  cursor: pointer;
  font-weight: 800;
}
.quiz-option.correct { border-color: rgba(74, 222, 128, 0.55); background: rgba(74, 222, 128, 0.12); }
.quiz-option.wrong { border-color: rgba(251, 113, 133, 0.55); background: rgba(251, 113, 133, 0.12); }
.quiz-option:disabled { cursor: default; opacity: .9; }
.quiz-feedback { display: none; margin-top: 12px; padding: 12px 14px; border-radius: 14px; font-weight: 800; }
.quiz-feedback.show { display:block; }
.quiz-feedback.ok { color: #bbf7d0; background: rgba(74,222,128,.10); border: 1px solid rgba(74,222,128,.28); }
.quiz-feedback.bad { color: #fecdd3; background: rgba(251,113,133,.10); border: 1px solid rgba(251,113,133,.28); }
.lesson-nav { display:flex; justify-content:space-between; gap: 12px; margin-top: 22px; }
.lesson-nav button, .lesson-nav a { min-height: 46px; padding: 0 18px; border-radius: 14px; display:inline-flex; align-items:center; justify-content:center; text-decoration:none; font-weight: 900; cursor: pointer; border: 1px solid var(--border); background: rgba(255,255,255,0.04); color: var(--text); }
.lesson-nav button.next, .lesson-nav a.next { background: var(--amber); color: #111827; border-color: rgba(255,255,255,.18); }
.lesson-nav button:disabled { opacity:.45; cursor:not-allowed; }

@media (max-width: 920px) {
  .hero, .layout { grid-template-columns: 1fr; }
  .sidebar { display: none; }
  .mobile-select-wrap { display: block; }
  .parts-grid, .grid-2 { grid-template-columns: 1fr; }
}
@media (max-width: 560px) {
  header { padding-top: 54px; }
  .layout, .mobile-select-wrap { width: min(100% - 28px, 1180px); }
  .progress-wrap { padding: 10px 14px; gap: 8px; }
  .progress-label { display:none; }
  .lesson-nav { flex-direction: column; }
  .back-link { left: 14px; bottom: 14px; }
}