:root {
  --bg: #0c1114;
  --surface: #151c20;
  --surface-2: #1c252a;
  --surface-3: #10171b;
  --line: #34434b;
  --line-strong: #53646d;
  --text: #f4f7f8;
  --muted: #acbac1;
  --green: #61e3a5;
  --blue: #6bbcff;
  --yellow: #ffd166;
  --red: #ff8585;
  --ink: #0b1114;
  --code: #090e11;
  --content: 1180px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  overflow-x: hidden;
  background: var(--bg);
  color: var(--text);
  font-family: Inter, system-ui, -apple-system, "Segoe UI", Arial, sans-serif;
  line-height: 1.65;
}

button, input, select { font: inherit; }
a { color: var(--blue); }
img { display: block; max-width: 100%; }
code, pre, .mono { font-family: Consolas, "Courier New", monospace; }

a:focus-visible, button:focus-visible, input:focus-visible, select:focus-visible,
summary:focus-visible {
  outline: 3px solid rgba(107, 188, 255, .42);
  outline-offset: 3px;
}

.site-header {
  position: sticky;
  z-index: 30;
  top: 0;
  border-bottom: 1px solid var(--line);
  background: rgba(12, 17, 20, .96);
  backdrop-filter: blur(12px);
}

.topbar {
  display: flex;
  width: min(var(--content), 100%);
  min-height: 60px;
  margin: 0 auto;
  padding: 0 20px;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--text);
  font-weight: 900;
  text-decoration: none;
}

.brand-mark {
  display: grid;
  width: 34px;
  height: 34px;
  place-items: center;
  border: 1px solid #4a725f;
  border-radius: 6px;
  background: #143426;
  color: var(--green);
  font: 900 .86rem/1 Consolas, monospace;
}

.topnav { display: flex; align-items: center; gap: 6px; }
.topnav a {
  padding: 7px 9px;
  border-radius: 5px;
  color: var(--muted);
  font-size: .86rem;
  font-weight: 800;
  text-decoration: none;
}
.topnav a:hover { background: var(--surface-2); color: var(--text); }

.layout {
  display: grid;
  width: min(var(--content), 100%);
  margin: 0 auto;
  padding: 26px 20px 68px;
  grid-template-columns: 238px minmax(0, 1fr);
  gap: 30px;
}
.layout > *, .home-intro > *, .section-head > * { min-width: 0; }

.sidebar {
  position: sticky;
  top: 84px;
  max-height: calc(100vh - 108px);
  overflow-x: hidden;
  overflow-y: auto;
  align-self: start;
  padding-right: 10px;
}

.sidebar-title {
  margin: 0 0 9px;
  color: var(--muted);
  font-size: .72rem;
  font-weight: 900;
  text-transform: uppercase;
}

.course-menu { display: grid; gap: 3px; }
.course-menu a {
  display: grid;
  grid-template-columns: 28px minmax(0, 1fr);
  gap: 7px;
  padding: 8px;
  border-left: 2px solid transparent;
  color: var(--muted);
  font-size: .81rem;
  line-height: 1.3;
  text-decoration: none;
}
.course-menu a:hover { color: var(--text); background: var(--surface); }
.course-menu a.active { border-left-color: var(--green); background: #14231d; color: var(--text); }
.menu-number { color: var(--green); font-family: Consolas, monospace; }
.sidebar-extra { display: grid; gap: 5px; margin-top: 18px; padding-top: 16px; border-top: 1px solid var(--line); }
.sidebar-extra a { padding: 7px 8px; color: var(--muted); font-size: .8rem; font-weight: 800; text-decoration: none; }
.sidebar-extra a:hover { color: var(--blue); }

.main { min-width: 0; }
.lesson-header { padding: 10px 0 28px; }
.eyebrow {
  margin: 0 0 7px;
  color: var(--green);
  font-size: .77rem;
  font-weight: 900;
  text-transform: uppercase;
}

h1, h2, h3, h4, p { margin-top: 0; }
h1 {
  max-width: 920px;
  margin-bottom: 12px;
  font-size: clamp(2rem, 4vw, 3.25rem);
  line-height: 1.07;
  letter-spacing: 0;
}
h2 { margin-bottom: 12px; font-size: 1.48rem; line-height: 1.2; letter-spacing: 0; }
h3 { margin-bottom: 8px; font-size: 1.06rem; letter-spacing: 0; }
h4 { margin-bottom: 6px; font-size: .95rem; letter-spacing: 0; }
p { color: var(--muted); }
.lead { max-width: 860px; margin-bottom: 0; color: #d7dfe3; font-size: 1.05rem; }

.lesson-meta { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 18px; }
.badge, .status-badge {
  display: inline-flex;
  min-height: 30px;
  padding: 4px 9px;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: 5px;
  color: var(--muted);
  font-size: .78rem;
  font-weight: 800;
}
.badge.green { border-color: #416b57; color: var(--green); }
.badge.yellow { border-color: #6b5d36; color: var(--yellow); }
.progress-track { height: 4px; margin-top: 22px; overflow: hidden; background: var(--surface-2); }
.progress-track span { display: block; height: 100%; background: var(--green); }

.band { min-width: 0; padding: 30px 0; border-top: 1px solid var(--line); }
.band > :last-child { margin-bottom: 0; }
.two-col { display: grid; grid-template-columns: minmax(0, 1fr) minmax(300px, .85fr); gap: 28px; align-items: start; }
.three-col { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 12px; }
.concept-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 11px; }

.concept-card, .problem-card, .metric-card {
  min-width: 0;
  padding: 15px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--surface);
}
.concept-card h3, .problem-card h3 { color: var(--text); }
.concept-card p, .problem-card p { margin-bottom: 0; font-size: .92rem; }
.concept-card.accent { border-top: 3px solid var(--green); }
.concept-card.blue { border-top: 3px solid var(--blue); }
.concept-card.yellow { border-top: 3px solid var(--yellow); }
.concept-card.red { border-top: 3px solid var(--red); }

.flow { display: flex; flex-wrap: wrap; gap: 8px; margin: 18px 0; align-items: center; }
.flow-step {
  padding: 9px 11px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: var(--surface);
  color: var(--muted);
  font-size: .82rem;
  font-weight: 800;
}
.flow-step.active { border-color: var(--yellow); background: #332c16; color: var(--yellow); }
.flow-step.done { border-color: #416b57; background: #14271e; color: var(--green); }
.flow-step.pruned { border-color: #704247; background: #2b1a1e; color: var(--red); text-decoration: line-through; }
.flow-arrow { color: var(--green); font-weight: 900; }

.note, .warning, .success {
  margin: 16px 0;
  padding: 14px 16px;
  border-radius: 6px;
  color: var(--muted);
}
.note { border-left: 3px solid var(--blue); background: #142633; }
.warning { border-left: 3px solid var(--red); background: #2b1a1e; }
.success { border-left: 3px solid var(--green); background: #14271e; }
.note strong { color: var(--blue); }
.warning strong { color: var(--red); }
.success strong { color: var(--green); }

.clean-list, .steps, .sources, .error-list, .check-list { display: grid; gap: 9px; margin: 0; padding: 0; list-style: none; }
.clean-list li, .steps li, .error-list li, .check-list li { padding: 10px 0 10px 15px; border-left: 3px solid var(--blue); color: var(--muted); }
.steps { counter-reset: steps; }
.steps li { counter-increment: steps; }
.steps li::before { content: counter(steps) ". "; color: var(--yellow); font-weight: 900; }
.clean-list strong, .steps strong, .error-list strong, .check-list strong { color: var(--text); }
.error-list li { border-left-color: var(--red); }
.check-list li { border-left-color: var(--green); }
.check-list li::before { content: "✓ "; color: var(--green); font-weight: 900; }

.code-shell { overflow: hidden; border: 1px solid var(--line); border-radius: 7px; background: var(--code); }
.code-head { display: flex; padding: 9px 13px; align-items: center; justify-content: space-between; gap: 12px; border-bottom: 1px solid var(--line); color: var(--muted); font-size: .78rem; }
pre { margin: 0; padding: 16px; overflow-x: auto; color: #dce5e9; font: .88rem/1.65 Consolas, "Courier New", monospace; tab-size: 4; }
.copy-btn { padding: 5px 8px; border: 1px solid var(--line); border-radius: 4px; background: var(--surface-2); color: var(--text); cursor: pointer; font-size: .75rem; font-weight: 800; }
.copy-btn:hover { border-color: var(--blue); }
.code-note { padding: 10px 14px; border-top: 1px solid var(--line); color: var(--muted); font-size: .82rem; }

.table-wrap { max-width: 100%; overflow-x: auto; border: 1px solid var(--line); border-radius: 7px; }
table { width: 100%; border-collapse: collapse; font-size: .9rem; }
th, td { padding: 10px 12px; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
th { background: var(--surface-2); color: var(--text); font-size: .77rem; text-transform: uppercase; }
td { color: var(--muted); }
tr:last-child td { border-bottom: 0; }
tr.trace-active td { background: #332c16; color: var(--yellow); }

.diagram {
  min-width: 0;
  overflow-x: auto;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--surface-3);
}
.diagram img { width: 100%; min-width: 520px; }
.tree { display: grid; gap: 10px; min-width: 520px; text-align: center; }
.tree-level { display: flex; justify-content: center; gap: 12px; }
.tree-node { min-width: 92px; padding: 8px 10px; border: 1px solid var(--line-strong); border-radius: 5px; background: var(--surface-2); color: var(--text); font: 800 .82rem/1.2 Consolas, monospace; }
.tree-node.repeat { border-color: var(--yellow); color: var(--yellow); }
.tree-node.pruned { border-color: var(--red); color: var(--red); opacity: .62; text-decoration: line-through; }
.tree-node.done { border-color: var(--green); background: #143426; color: var(--green); }

.lab { overflow: hidden; border: 1px solid var(--line); border-radius: 8px; background: var(--surface); }
.lab-header { display: flex; padding: 14px 16px; align-items: center; justify-content: space-between; gap: 15px; border-bottom: 1px solid var(--line); }
.lab-header h2 { margin: 0; font-size: 1.08rem; }
.lab-kicker { color: var(--green); font-size: .73rem; font-weight: 900; text-transform: uppercase; }
.lab-body { min-height: 245px; padding: 18px 16px; }
.lab-controls { display: flex; flex-wrap: wrap; gap: 10px; padding: 13px 16px; border-top: 1px solid var(--line); background: var(--surface-2); }
.field { display: grid; flex: 1 1 180px; gap: 4px; min-width: 0; }
.field label { color: var(--muted); font-size: .72rem; font-weight: 900; text-transform: uppercase; }
.field input, .field select {
  width: 100%;
  min-height: 42px;
  padding: 8px 10px;
  border: 1px solid var(--line-strong);
  border-radius: 5px;
  background: #0d1418;
  color: var(--text);
}
.btn { display: inline-flex; min-height: 42px; padding: 8px 13px; align-items: center; justify-content: center; gap: 7px; border: 1px solid var(--line-strong); border-radius: 6px; background: #27333a; color: var(--text); font-weight: 850; text-decoration: none; cursor: pointer; }
.btn:hover { border-color: var(--blue); }
.btn.primary { border-color: var(--green); background: var(--green); color: var(--ink); }
.btn.secondary { border-color: #685a34; background: #332d1c; color: var(--yellow); }
.btn.danger { border-color: #704247; background: #351c20; color: var(--red); }
.btn:disabled { opacity: .42; cursor: default; }
.btn-row { display: flex; flex-wrap: wrap; gap: 9px; }
.icon-btn { width: 42px; padding: 0; font-size: 1.15rem; }
.lab-message { min-height: 46px; margin-top: 14px; padding: 11px 13px; border-left: 3px solid var(--green); background: var(--surface-3); color: var(--muted); }
.lab-message strong { color: var(--text); }
.metrics { display: grid; grid-template-columns: repeat(auto-fit, minmax(130px, 1fr)); gap: 8px; margin-bottom: 14px; }
.metric-card span { display: block; color: var(--muted); font-size: .72rem; font-weight: 800; text-transform: uppercase; }
.metric-card strong { display: block; margin-top: 4px; color: var(--yellow); font: 900 1.08rem/1.2 Consolas, monospace; }
.tokens { display: flex; min-height: 72px; flex-wrap: wrap; gap: 7px; align-content: flex-start; }
.token { display: grid; min-width: 50px; min-height: 50px; padding: 6px 8px; place-items: center; border: 1px solid var(--line-strong); border-radius: 5px; background: var(--surface-2); color: var(--text); font: 850 .92rem/1 Consolas, monospace; }
.token.active { border-color: var(--yellow); background: #3a3117; color: var(--yellow); }
.token.done { border-color: #416a57; background: #153426; color: var(--green); }
.token.bad { border-color: #704247; background: #351c20; color: var(--red); }
.token small { display: block; color: var(--muted); font-size: .62rem; }
.stack-view { display: flex; min-height: 260px; flex-direction: column-reverse; justify-content: flex-start; gap: 6px; padding: 14px; border: 1px dashed var(--line-strong); background: var(--surface-3); }
.stack-frame { width: min(100%, 430px); margin: 0 auto; padding: 10px 12px; border: 1px solid var(--blue); border-radius: 5px; background: #142633; color: var(--text); font: 800 .84rem/1.3 Consolas, monospace; }
.stack-frame.active { border-color: var(--yellow); background: #332c16; color: var(--yellow); }
.interval { display: grid; grid-template-columns: repeat(8, minmax(46px, 1fr)); gap: 5px; min-width: 520px; }
.interval-cell { display: grid; min-height: 58px; place-items: center; border: 1px solid var(--line); background: var(--surface-2); color: var(--muted); font: 850 .9rem/1 Consolas, monospace; }
.interval-cell.kept { border-color: var(--blue); color: var(--text); }
.interval-cell.mid { border-color: var(--yellow); background: #332c16; color: var(--yellow); }
.interval-cell.discarded { opacity: .3; text-decoration: line-through; }
.quiz-options { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 8px; }
.quiz-option { padding: 12px; border: 1px solid var(--line); border-radius: 6px; background: var(--surface-3); color: var(--text); text-align: left; cursor: pointer; }
.quiz-option:hover { border-color: var(--blue); }
.quiz-option.correct { border-color: var(--green); background: #14271e; }
.quiz-option.wrong { border-color: var(--red); background: #2b1a1e; }

.question-list { display: grid; gap: 8px; }
.question-list details { border: 1px solid var(--line); border-radius: 6px; background: var(--surface); }
.question-list summary { padding: 12px 14px; color: var(--text); font-weight: 800; cursor: pointer; }
.question-answer { padding: 0 14px 13px; color: var(--muted); }
.question-answer p:last-child { margin-bottom: 0; }

.sources li { color: var(--muted); }
.sources a { font-weight: 750; }
.source-note { color: var(--muted); font-size: .83rem; }
.lesson-nav { display: grid; grid-template-columns: 1fr 1fr; gap: 11px; padding-top: 28px; border-top: 1px solid var(--line); }
.lesson-nav a { min-width: 0; padding: 12px 14px; border: 1px solid var(--line); border-radius: 6px; color: var(--text); font-weight: 850; text-decoration: none; }
.lesson-nav a:last-child { text-align: right; }
.lesson-nav a:hover { border-color: var(--blue); }

.home { width: min(var(--content), 100%); margin: 0 auto; padding: 36px 20px 70px; }
.home-intro { display: grid; min-height: 500px; grid-template-columns: minmax(0, 1fr) minmax(380px, .9fr); gap: 38px; align-items: center; }
.hero-visual { min-width: 0; margin: 0; overflow: hidden; }
.hero-visual img { width: 100%; max-height: 430px; }
.home-actions { display: flex; flex-wrap: wrap; gap: 9px; margin-top: 22px; }
.home-section { padding: 34px 0; border-top: 1px solid var(--line); }
.section-head { display: flex; margin-bottom: 18px; justify-content: space-between; gap: 24px; align-items: end; }
.section-head > p { max-width: 590px; margin-bottom: 0; }
.lesson-grid, .study-grid, .paradigm-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 11px; }
.lesson-link, .study-link, .paradigm-link {
  display: grid;
  min-width: 0;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--surface);
  color: var(--text);
  text-decoration: none;
}
.lesson-link { grid-template-columns: 54px minmax(0, 1fr); column-gap: 13px; }
.lesson-link:hover, .study-link:hover, .paradigm-link:hover { border-color: var(--blue); background: var(--surface-2); }
.lesson-number { grid-row: 1 / span 2; color: var(--green); font: 900 .84rem/1.3 Consolas, monospace; }
.lesson-link strong, .study-link strong, .paradigm-link strong { color: var(--text); }
.lesson-link span:last-child, .study-link span, .paradigm-link span { color: var(--muted); font-size: .84rem; }
.study-link { gap: 4px; }
.source-strip { display: flex; flex-wrap: wrap; gap: 8px; }
.source-strip a { padding: 8px 10px; border: 1px solid var(--line); border-radius: 5px; color: var(--muted); font-size: .82rem; font-weight: 800; text-decoration: none; }
.source-strip a:hover { color: var(--blue); }

.catalog { width: min(var(--content), 100%); margin: 0 auto; padding: 34px 20px 70px; }
.catalog-head { margin-bottom: 26px; }
.filter-bar { display: grid; grid-template-columns: repeat(4, minmax(150px, 1fr)); gap: 10px; padding: 14px; border: 1px solid var(--line); background: var(--surface); }
.filter-bar.two-filters { grid-template-columns: repeat(2, minmax(180px, 1fr)); }
.filter-bar .field { width: 100%; }
.catalog-summary { display: flex; flex-wrap: wrap; gap: 8px; margin: 18px 0; }
.exercise-grid { display: grid; gap: 10px; }
.exercise-card { display: grid; grid-template-columns: 110px minmax(0, 1fr) 210px; gap: 15px; padding: 16px; border: 1px solid var(--line); border-radius: 7px; background: var(--surface); }
.exercise-id { color: var(--green); font: 900 .88rem/1.3 Consolas, monospace; }
.exercise-main h2 { margin: 0 0 5px; font-size: 1.08rem; }
.exercise-main p { margin-bottom: 8px; font-size: .88rem; }
.exercise-tags { display: flex; flex-wrap: wrap; gap: 5px; }
.tag { padding: 3px 7px; border: 1px solid var(--line); border-radius: 4px; color: var(--muted); font-size: .7rem; font-weight: 800; }
.exercise-side { display: grid; align-content: start; justify-items: start; gap: 8px; }
.status-badge.waiting { border-color: #6b5d36; background: #292418; color: var(--yellow); }
.status-badge.validated { border-color: #416b57; background: #14271e; color: var(--green); }
.exercise-meta { display: grid; grid-template-columns: auto 1fr; gap: 4px 8px; margin: 8px 0 0; color: var(--muted); font-size: .8rem; }
.exercise-meta dt { color: var(--text); font-weight: 800; }
.exercise-meta dd { margin: 0; }
.empty-state { padding: 28px; border: 1px dashed var(--line-strong); color: var(--muted); text-align: center; }
.validation-flow { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 7px; }
.validation-step { padding: 12px; border: 1px solid var(--line); background: var(--surface); color: var(--muted); font-size: .82rem; }
.validation-step strong { display: block; margin-bottom: 3px; color: var(--green); }

.site-footer { border-top: 1px solid var(--line); }
.site-footer-inner { display: flex; width: min(var(--content), 100%); margin: 0 auto; padding: 22px 20px; justify-content: space-between; gap: 15px; color: var(--muted); font-size: .82rem; }

@media (max-width: 960px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { position: static; max-height: none; padding: 0 0 18px; border-bottom: 1px solid var(--line); }
  .course-menu { display: flex; width: 100%; max-width: calc(100vw - 40px); overflow-x: auto; padding-bottom: 6px; }
  .course-menu a { min-width: 185px; border-left: 0; border-bottom: 2px solid transparent; }
  .course-menu a.active { border-left: 0; border-bottom-color: var(--green); }
  .sidebar-extra { display: flex; overflow-x: auto; }
  .home-intro { min-height: 0; grid-template-columns: 1fr; }
  .hero-visual { max-width: 680px; }
  .exercise-card { grid-template-columns: 100px minmax(0, 1fr); }
  .exercise-side { grid-column: 2; }
  .filter-bar { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 680px) {
  .topbar { min-height: 54px; padding: 0 14px; }
  .brand span:last-child { display: none; }
  .topnav a { padding: 6px; font-size: .76rem; }
  .layout, .home, .catalog { padding-right: 14px; padding-left: 14px; }
  h1 { font-size: 2.05rem; }
  .home-intro { display: block; }
  .home-intro h1, .lesson-header h1 { overflow-wrap: anywhere; }
  .hero-visual { width: 100%; margin-top: 34px; }
  .lesson-meta > * { max-width: 100%; }
  .course-menu { max-width: calc(100vw - 28px); }
  .two-col, .three-col, .concept-grid, .lesson-grid, .study-grid, .paradigm-grid, .quiz-options { grid-template-columns: 1fr; }
  .section-head { display: block; }
  .section-head > p { margin-top: 8px; }
  .filter-bar { grid-template-columns: 1fr; }
  .filter-bar.two-filters { grid-template-columns: 1fr; }
  .exercise-card { grid-template-columns: 1fr; }
  .exercise-side { grid-column: 1; }
  .validation-flow { grid-template-columns: 1fr; }
  .lesson-nav { grid-template-columns: 1fr; }
  .lesson-nav a:last-child { text-align: left; }
  .site-footer-inner { flex-direction: column; }
  .lab-controls .btn { flex: 1 1 120px; }
  .field { flex-basis: 100%; }
}

@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }