:root {
  --bg: #f6f7f3;
  --paper: #fffdf8;
  --ink: #24313a;
  --muted: #63727a;
  --line: #d9dfd7;
  --green: #19705f;
  --green-dark: #0f5146;
  --blue: #2f63b8;
  --amber: #b46b20;
  --rose: #ad4d63;
  --code: #142432;
  --soft-green: #e8f3ef;
  --soft-blue: #e9f0fb;
  --soft-amber: #fff1dc;
  --shadow: 0 10px 28px rgba(39, 52, 57, .08);
  --mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 88px;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--bg);
  font: 16px/1.78 var(--sans);
}

a {
  color: var(--green-dark);
  text-underline-offset: 4px;
}

button,
summary {
  cursor: pointer;
}

button,
.button,
.source-link {
  border: 1px solid var(--green);
  border-radius: 8px;
  background: var(--paper);
  color: var(--green-dark);
  padding: 8px 14px;
  font: 700 14px/1 var(--sans);
  text-decoration: none;
}

button:hover,
.button:hover,
.source-link:hover {
  background: var(--soft-green);
}

button:disabled {
  opacity: .55;
  cursor: not-allowed;
}

:focus-visible {
  outline: 3px solid rgba(47, 99, 184, .45);
  outline-offset: 3px;
}

code {
  font-family: var(--mono);
}

p code,
li code,
summary code {
  background: #edf1ed;
  border-radius: 4px;
  padding: 1px 5px;
  font-size: .92em;
}

pre {
  margin: 18px 0 0;
  padding: 18px;
  overflow: auto;
  border-radius: 8px;
  background: var(--code);
  color: #edf7fa;
  font: 14px/1.75 var(--mono);
  tab-size: 4;
}

.skip {
  position: absolute;
  top: -100px;
  left: 16px;
  z-index: 100;
  background: var(--paper);
  padding: 10px 14px;
}

.skip:focus {
  top: 12px;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 18px;
  padding: 14px 28px;
  border-bottom: 1px solid var(--line);
  background: rgba(255, 253, 248, .95);
  backdrop-filter: blur(10px);
}

.brand {
  margin-right: auto;
  color: var(--ink);
  font-weight: 800;
  text-decoration: none;
}

.topbar nav {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
  font-size: 14px;
}

.hero,
.band,
.footer {
  max-width: 1120px;
  margin: 0 auto;
  padding-inline: 28px;
}

.hero {
  padding-top: 58px;
  padding-bottom: 34px;
}

.eyebrow,
.section-kicker {
  margin: 0 0 8px;
  color: var(--green);
  font: 800 13px/1.2 var(--mono);
  text-transform: uppercase;
  letter-spacing: .08em;
}

h1,
h2,
h3 {
  line-height: 1.35;
  letter-spacing: 0;
}

h1 {
  margin: 0 0 12px;
  font-size: clamp(34px, 6vw, 58px);
}

h2 {
  margin: 0 0 12px;
  font-size: clamp(25px, 3vw, 34px);
}

h3 {
  margin: 0 0 10px;
  font-size: 21px;
}

p {
  margin: 10px 0;
}

.lead {
  max-width: 800px;
  color: var(--muted);
  font-size: 18px;
}

.hero-actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 22px;
}

.button.primary {
  background: var(--green);
  color: white;
}

.button.primary:hover {
  background: var(--green-dark);
}

.band {
  padding-top: 30px;
  padding-bottom: 34px;
}

.intro-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(290px, .85fr);
  gap: 24px;
  align-items: start;
}

.learning-steps {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 10px;
}

.learning-steps li,
.module,
.note,
.deep-dive,
.road-card {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
  box-shadow: var(--shadow);
}

.learning-steps li {
  display: grid;
  grid-template-columns: 38px minmax(0, 1fr);
  gap: 8px 12px;
  padding: 14px;
}

.learning-steps span {
  grid-row: span 2;
  width: 32px;
  height: 32px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--soft-green);
  color: var(--green-dark);
  font-weight: 800;
}

.learning-steps strong {
  line-height: 1.3;
}

.learning-steps small {
  color: var(--muted);
}

.section-heading {
  max-width: 820px;
  margin-bottom: 18px;
}

.roadmap {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
}

.road-card {
  display: grid;
  gap: 8px;
  min-height: 210px;
  padding: 16px;
  width: 100%;
  text-align: left;
  text-decoration: none;
  color: var(--ink);
  font: inherit;
}

.road-card:hover {
  border-color: rgba(25, 112, 95, .55);
}

.road-card.disabled {
  opacity: .55;
}

.road-card .meta {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  align-items: center;
  color: var(--muted);
  font: 700 12px var(--mono);
}

.tag {
  display: inline-flex;
  align-items: center;
  min-height: 22px;
  border-radius: 999px;
  padding: 2px 8px;
  background: var(--soft-blue);
  color: var(--blue);
  font-size: 12px;
  font-weight: 800;
}

.tag.easy {
  background: var(--soft-green);
  color: var(--green-dark);
}

.tag.hard {
  background: #f8e7eb;
  color: var(--rose);
}

.ready-tag {
  background: #edf1ed;
  color: var(--green-dark);
}

.road-card h3 {
  font-size: 18px;
  margin: 0;
}

.road-card p {
  margin: 0;
  color: var(--muted);
  font-size: 14px;
}

.roadmap-more {
  margin-top: 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
  padding: 0 16px 16px;
}

.roadmap-more summary {
  padding: 16px 0;
  color: var(--green-dark);
  font-weight: 800;
}

.roadmap-more > p {
  margin: -2px 0 16px;
  color: var(--muted);
  font-size: 14px;
}

.advanced-roadmap {
  border-top: 1px solid var(--line);
  padding-top: 16px;
}

.lesson-head {
  display: flex;
  gap: 20px;
  justify-content: space-between;
  align-items: start;
  margin-bottom: 18px;
}

.source-link {
  white-space: nowrap;
  margin-top: 6px;
}

.lesson-shell {
  display: grid;
  grid-template-columns: 300px minmax(0, 1fr);
  gap: 18px;
  align-items: start;
}

.lesson-nav {
  position: sticky;
  top: 82px;
  display: grid;
  gap: 8px;
}

.lesson-panel {
  min-width: 0;
}

.lesson-picker {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 18px;
}

.lesson-tab.active {
  background: var(--green);
  color: white;
}

.lesson-tabs {
  display: grid;
  grid-template-columns: repeat(6, minmax(0, 1fr));
  gap: 10px;
  margin: 18px 0;
}

.lesson-tab {
  min-height: 104px;
  display: grid;
  align-content: start;
  gap: 6px;
  text-align: left;
  white-space: normal;
  width: 100%;
}

.lesson-tab span,
.lesson-tab small {
  color: var(--muted);
  font: 700 12px/1.35 var(--sans);
}

.lesson-tab strong {
  color: var(--ink);
  font-size: 18px;
}

.lesson-tab.active {
  background: var(--green);
  border-color: var(--green-dark);
  color: white;
}

.lesson-tab.active span,
.lesson-tab.active strong,
.lesson-tab.active small {
  color: white;
}

.module,
.note,
.deep-dive {
  margin-top: 16px;
  padding: 22px;
}

.lesson-facts {
  display: grid;
  grid-template-columns: .6fr 1.4fr 1.4fr;
  gap: 10px;
  margin: 14px 0;
}

.lesson-facts div {
  min-height: 82px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
  padding: 12px;
  box-shadow: var(--shadow);
}

.lesson-facts span {
  display: block;
  color: var(--muted);
  font-size: 12px;
}

.lesson-facts strong {
  display: block;
  margin-top: 6px;
  font-size: 14px;
  line-height: 1.45;
}

.takeaways {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin: 10px 0 16px;
}

.takeaways span {
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--soft-blue);
  color: var(--blue);
  padding: 4px 10px;
  font-size: 13px;
  font-weight: 800;
}

.manual-table {
  display: grid;
  gap: 8px;
  margin-top: 16px;
}

.manual-table div {
  display: grid;
  grid-template-columns: 88px minmax(0, 1fr) 56px;
  gap: 12px;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  background: #fcfbf4;
}

.manual-table strong {
  color: var(--amber);
  text-align: right;
}

.demo-module {
  display: grid;
  grid-template-columns: minmax(0, .9fr) minmax(340px, 1.1fr);
  gap: 18px;
}

.demo {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fbfcff;
  padding: 16px;
}

.demo h4 {
  margin: 0 0 12px;
  font-size: 17px;
}

.visual-row {
  display: grid;
  gap: 8px;
  margin-bottom: 12px;
}

.row-label {
  color: var(--muted);
  font: 800 12px/1.2 var(--mono);
}

.cell-track {
  display: grid;
  grid-template-columns: repeat(var(--cell-count), minmax(54px, 1fr));
  gap: 8px;
  overflow-x: auto;
  padding-bottom: 2px;
}

.visual-cell {
  position: relative;
  min-width: 54px;
  min-height: 82px;
  display: grid;
  grid-template-rows: 18px 1fr 16px 18px;
  align-items: center;
  justify-items: center;
  border: 2px solid #c9d2db;
  border-radius: 8px;
  background: white;
}

.visual-cell.active {
  border-color: var(--amber);
  background: var(--soft-amber);
}

.visual-cell.match {
  border-color: var(--green);
  background: var(--soft-green);
}

.visual-cell.mismatch {
  border-color: var(--rose);
  background: #f8e7eb;
}

.visual-cell.chosen {
  border-color: var(--blue);
  background: var(--soft-blue);
}

.visual-cell.discarded,
.visual-cell.muted {
  opacity: .58;
}

.visual-cell.best {
  border-color: var(--green-dark);
  background: #dceee8;
}

.cell-value {
  font: 800 24px/1 var(--mono);
}

.cell-index,
.pointer {
  color: var(--muted);
  font: 800 11px/1 var(--mono);
}

.pointer {
  color: var(--green-dark);
}

.secondary .cell-value {
  font-size: 18px;
}

.demo-label {
  min-height: 22px;
  color: var(--muted);
  font: 800 12px/1.3 var(--mono);
}

.string-row {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(42px, 1fr));
  gap: 7px;
  margin-bottom: 16px;
}

.lesson-string-row {
  grid-template-columns: repeat(3, minmax(46px, 1fr));
  max-width: 100%;
  overflow-x: auto;
  padding: 12px 2px;
}

.secondary-row {
  margin-top: -4px;
}

.char-cell {
  position: relative;
  min-height: 64px;
  display: grid;
  align-content: center;
  justify-items: center;
  border: 2px solid #c9d2db;
  border-radius: 8px;
  background: white;
}

.char-cell.active {
  border-color: var(--amber);
  background: var(--soft-amber);
}

.char-cell.in-range,
.char-cell.match,
.char-cell.chosen {
  border-color: var(--green);
  background: var(--soft-green);
}

.char-cell.mismatch {
  border-color: var(--rose);
  background: #f8e7eb;
}

.char-cell.discarded,
.char-cell.muted {
  color: var(--muted);
  background: #eef1ef;
  opacity: .72;
}

.char-cell.best {
  border-color: var(--blue);
  background: var(--soft-blue);
}

.char-cell .char {
  font: 800 22px/1 var(--mono);
  overflow-wrap: anywhere;
}

.char-cell .idx {
  margin-top: 7px;
  color: var(--muted);
  font: 700 12px/1 var(--mono);
}

.pointer {
  position: absolute;
  left: 50%;
  translate: -50% 0;
  min-width: 24px;
  border-radius: 999px;
  padding: 2px 7px;
  background: var(--ink);
  color: white;
  font: 800 11px/1.35 var(--mono);
}

.pointer.top {
  top: -10px;
}

.pointer.bottom {
  bottom: -10px;
}

.demo-status {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 8px;
}

.demo-status div {
  min-height: 76px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px;
  background: white;
}

.demo-status span {
  display: block;
  color: var(--muted);
  font-size: 12px;
}

.demo-status strong {
  display: block;
  margin-top: 4px;
  font: 800 18px/1.25 var(--mono);
  overflow-wrap: anywhere;
}

.frame-note {
  min-height: 58px;
  margin: 14px 0;
  color: var(--ink);
}

.chip-row {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  min-height: 28px;
  margin: 12px 0;
}

.chip-row span {
  border: 1px solid var(--line);
  border-radius: 999px;
  background: white;
  padding: 2px 8px;
  color: var(--green-dark);
  font: 800 12px/1.6 var(--mono);
}

.chip-row {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  min-height: 28px;
  margin: -4px 0 12px;
}

.chip-row span {
  border-radius: 999px;
  background: var(--soft-green);
  color: var(--green-dark);
  padding: 3px 8px;
  font: 800 12px/1.4 var(--mono);
}

.controls {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.controls button {
  min-width: 52px;
}

.progress {
  height: 8px;
  margin-top: 12px;
  border-radius: 999px;
  background: #e1e6ea;
  overflow: hidden;
}

.progress i {
  display: block;
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, var(--green), var(--blue));
}

.tests {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
  margin-top: 12px;
}

.test-case {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  background: #fcfbf4;
}

.test-case code {
  display: block;
  margin-bottom: 4px;
  font-weight: 800;
}

.deep-dive summary {
  color: var(--green-dark);
  font-weight: 800;
}

.note {
  background: var(--soft-blue);
  border-color: #cbd8ef;
}

.unavailable {
  background: #fcfbf4;
}

.footer {
  padding-top: 14px;
  padding-bottom: 42px;
  color: var(--muted);
  font-size: 14px;
}

@media (max-width: 860px) {
  .topbar {
    align-items: flex-start;
    flex-direction: column;
    gap: 8px;
    padding-inline: 18px;
  }

  .brand {
    margin-right: 0;
  }

  .hero,
  .band,
  .footer {
    padding-inline: 18px;
  }

  .intro-grid,
  .demo-module,
  .lesson-head {
    display: block;
  }

  .lesson-shell {
    display: block;
  }

  .lesson-nav {
    position: static;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    margin-bottom: 16px;
  }

  .lesson-facts {
    grid-template-columns: 1fr;
  }

  .source-link {
    display: inline-flex;
    margin: 8px 0 0;
  }

  .roadmap {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .lesson-tabs {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .demo {
    margin-top: 14px;
  }
}

@media (max-width: 560px) {
  body {
    font-size: 15px;
  }

  .roadmap,
  .tests {
    grid-template-columns: 1fr;
  }

  .lesson-tabs {
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 6px;
  }

  .lesson-tab {
    min-height: 72px;
    padding: 8px;
  }

  .lesson-tab span {
    font-size: 10px;
  }

  .lesson-tab strong {
    font-size: 15px;
  }

  .lesson-tab small {
    display: none;
  }

  .lesson-nav {
    grid-template-columns: 1fr;
  }

  .manual-table div {
    grid-template-columns: 1fr;
    gap: 5px;
  }

  .manual-table strong {
    text-align: left;
  }

  .string-row {
    grid-template-columns: repeat(auto-fit, minmax(36px, 1fr));
    gap: 5px;
  }

  .cell-track {
    grid-template-columns: repeat(var(--cell-count), minmax(48px, 1fr));
    gap: 6px;
  }

  .visual-cell {
    min-width: 48px;
    min-height: 74px;
  }

  .cell-value {
    font-size: 20px;
  }

  .char-cell {
    min-height: 58px;
  }

  .char-cell .char {
    font-size: 19px;
  }

  .demo-status {
    grid-template-columns: 1fr;
  }

  .controls button {
    flex: 1 1 76px;
  }

  pre {
    padding: 14px;
    font-size: 12px;
  }
}

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

.mini-link {
  display: inline-flex;
  align-items: center;
  min-height: 33px;
  border: 1px solid var(--green);
  border-radius: 8px;
  background: var(--paper);
  color: var(--green-dark);
  padding: 8px 14px;
  font: 700 14px/1 var(--sans);
  text-decoration: none;
}

.mini-link:hover {
  background: var(--soft-green);
}

.card-actions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  align-items: center;
  margin-top: 4px;
}

.road-card.is-pending {
  opacity: .78;
}

.lesson-placeholder {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
  box-shadow: var(--shadow);
  margin-top: 16px;
  padding: 22px;
}

.lesson-tabs button.active {
  background: var(--green);
  color: white;
}

.generic-row {
  grid-template-columns: repeat(var(--cell-count), minmax(58px, 1fr));
  overflow-x: auto;
  padding: 10px 2px 12px;
}

.secondary-label {
  margin-top: 12px;
}

.secondary-row .char-cell {
  min-height: 64px;
}

.secondary-row .char-cell .char {
  font-size: 20px;
}

.chips {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  min-height: 30px;
  margin-bottom: 12px;
}

.chips span {
  display: inline-flex;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: white;
  padding: 2px 8px;
  color: var(--green-dark);
  font: 700 12px/1.5 var(--mono);
}