:root {
  color-scheme: light;
  --ink: #17211b;
  --muted: #68716b;
  --paper: #f5f5ef;
  --surface: #ffffff;
  --line: #dfe2db;
  --green: #3cff88;
  --green-deep: #0f8a4c;
  --orange: #ff7c45;
  --yellow: #f4d44d;
  --blue: #6f8cff;
  --pink: #ff7597;
  --shadow: 0 18px 50px rgba(25, 38, 29, 0.08);
  --mono: "DM Mono", ui-monospace, SFMono-Regular, Menlo, monospace;
  --sans: "Manrope", system-ui, sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(circle at 85% 2%, rgba(60, 255, 136, 0.12), transparent 23rem),
    var(--paper);
  font-family: var(--sans);
  min-width: 320px;
}

button,
input {
  font: inherit;
}

button {
  color: inherit;
}

.app-shell {
  min-height: 100vh;
}

.topbar {
  height: 76px;
  padding: 0 clamp(24px, 5vw, 76px);
  border-bottom: 1px solid var(--line);
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  background: rgba(245, 245, 239, 0.86);
  backdrop-filter: blur(16px);
  position: sticky;
  top: 0;
  z-index: 20;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 11px;
  color: var(--ink);
  text-decoration: none;
  font-weight: 800;
  letter-spacing: -0.03em;
  font-size: 18px;
}

.brand-mark {
  width: 37px;
  height: 37px;
  border-radius: 11px;
  display: grid;
  place-items: center;
  background: var(--ink);
  color: var(--green);
  font-family: var(--mono);
  font-size: 16px;
  box-shadow: 4px 4px 0 var(--green);
}

.main-nav {
  display: flex;
  align-items: center;
  gap: 6px;
  background: rgba(224, 226, 218, 0.65);
  padding: 5px;
  border-radius: 12px;
}

.nav-link {
  border: 0;
  padding: 9px 16px;
  border-radius: 8px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  font-size: 13px;
  font-weight: 700;
}

.nav-link.active {
  background: var(--surface);
  color: var(--ink);
  box-shadow: 0 2px 8px rgba(20, 30, 23, 0.08);
}

.header-actions {
  justify-self: end;
  display: flex;
  align-items: center;
  gap: 10px;
}

.language-switch {
  display: flex;
  padding: 3px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--surface);
}

.language-button {
  width: 31px;
  height: 27px;
  padding: 0;
  border: 0;
  border-radius: 999px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  font-size: 9px;
  font-weight: 800;
}

.language-button.active {
  background: var(--ink);
  color: var(--surface);
}

.progress-pill {
  padding: 8px 12px;
  border: 1px solid var(--line);
  border-radius: 999px;
  font-size: 11px;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  background: var(--surface);
}

.icon-button {
  border: 1px solid var(--line);
  background: var(--surface);
  width: 36px;
  height: 36px;
  border-radius: 50%;
  cursor: pointer;
  font-size: 18px;
}

main {
  padding: 0 clamp(24px, 5vw, 76px);
}

.hero {
  max-width: 1400px;
  margin: 0 auto;
  padding: clamp(56px, 8vw, 104px) 0 44px;
  display: grid;
  grid-template-columns: 1.5fr 0.7fr;
  align-items: end;
  gap: 50px;
}

.eyebrow {
  margin: 0 0 14px;
  font-size: 11px;
  font-weight: 800;
  letter-spacing: 0.16em;
  color: var(--green-deep);
}

.hero h1 {
  margin: 0;
  max-width: 840px;
  font-size: clamp(44px, 6.2vw, 88px);
  line-height: 0.98;
  letter-spacing: -0.075em;
}

.hero h1 span {
  font-family: var(--mono);
  font-weight: 500;
  color: var(--green-deep);
  letter-spacing: -0.09em;
}

.hero-copy {
  color: var(--muted);
  line-height: 1.75;
  font-size: 15px;
  max-width: 430px;
  margin: 0 0 6px;
}

.view {
  display: none;
}

.view.active {
  display: block;
  animation: reveal 0.35s ease both;
}

@keyframes reveal {
  from { opacity: 0; transform: translateY(8px); }
}

.workspace {
  max-width: 1400px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: minmax(330px, 0.78fr) minmax(520px, 1.4fr);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 22px;
  overflow: hidden;
  box-shadow: var(--shadow);
}

.control-panel {
  padding: 32px;
  border-right: 1px solid var(--line);
}

.panel-heading {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 25px;
}

.panel-heading.compact {
  margin-bottom: 16px;
}

.panel-heading > div {
  display: flex;
  align-items: center;
  gap: 12px;
}

.step-number {
  color: var(--green-deep);
  font-size: 11px;
  font-weight: 800;
  border: 1px solid color-mix(in srgb, var(--green-deep) 35%, transparent);
  border-radius: 6px;
  padding: 4px 6px;
}

.panel-heading h3 {
  margin: 0;
  font-size: 16px;
}

.text-button,
.reset-button {
  border: 0;
  background: transparent;
  padding: 4px;
  cursor: pointer;
  color: var(--green-deep);
  font-size: 12px;
  font-weight: 800;
}

.field-label {
  display: block;
  margin-bottom: 8px;
  font-size: 10px;
  font-weight: 800;
  letter-spacing: 0.11em;
  text-transform: uppercase;
  color: var(--muted);
}

.regex-input-wrap {
  height: 57px;
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 0 15px;
  border: 1.5px solid var(--line);
  border-radius: 12px;
  background: #fafbf8;
  transition: border 0.2s, box-shadow 0.2s;
}

.regex-input-wrap:focus-within {
  border-color: var(--green-deep);
  box-shadow: 0 0 0 3px rgba(60, 255, 136, 0.16);
}

.regex-input-wrap.invalid {
  border-color: #df4e4e;
}

.slash {
  color: var(--green-deep);
  font-family: var(--mono);
  font-size: 20px;
}

.regex-input,
.flags-input {
  min-width: 0;
  border: 0;
  outline: 0;
  background: transparent;
  color: var(--ink);
  font-family: var(--mono);
  font-size: 15px;
}

.regex-input {
  flex: 1;
}

.flags-input {
  width: 28px;
  color: var(--green-deep);
}

.field-help {
  min-height: 18px;
  margin: 8px 0 18px;
  color: var(--muted);
  font-size: 11px;
}

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

.explanation-card {
  min-height: 74px;
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 15px;
  border-radius: 12px;
  background: color-mix(in srgb, var(--green) 10%, var(--paper));
}

.explanation-card p {
  margin: 0;
  color: color-mix(in srgb, var(--ink) 78%, var(--muted));
  font-size: 12px;
  line-height: 1.65;
}

.explanation-icon {
  color: var(--green-deep);
  font-size: 18px;
}

.divider {
  height: 1px;
  background: var(--line);
  margin: 27px 0;
}

.dataset-tabs {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 5px;
  padding: 5px;
  border-radius: 10px;
  background: var(--paper);
}

.dataset-tab {
  border: 0;
  background: transparent;
  border-radius: 7px;
  padding: 9px 4px;
  color: var(--muted);
  cursor: pointer;
  font-size: 11px;
  font-weight: 700;
}

.dataset-tab.active {
  background: var(--surface);
  color: var(--ink);
  box-shadow: 0 2px 7px rgba(25, 35, 28, 0.08);
}

.run-actions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 9px;
  margin-top: 24px;
}

.button {
  min-height: 48px;
  border-radius: 10px;
  border: 1px solid var(--line);
  cursor: pointer;
  padding: 0 17px;
  font-size: 12px;
  font-weight: 800;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
}

.button.primary {
  background: var(--ink);
  border-color: var(--ink);
  color: white;
  box-shadow: 4px 4px 0 var(--green);
}

.button.primary:hover {
  transform: translate(-1px, -1px);
  box-shadow: 6px 6px 0 var(--green);
}

.button.secondary {
  background: var(--surface);
}

.visual-stage {
  min-height: 590px;
  background:
    linear-gradient(rgba(23, 33, 27, 0.027) 1px, transparent 1px),
    linear-gradient(90deg, rgba(23, 33, 27, 0.027) 1px, transparent 1px),
    #f9faf6;
  background-size: 28px 28px;
  position: relative;
}

.stage-topbar {
  height: 55px;
  padding: 0 22px;
  border-bottom: 1px solid var(--line);
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: rgba(255, 255, 255, 0.74);
}

.stage-topbar > div {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 9px;
  font-weight: 800;
  letter-spacing: 0.12em;
}

.live-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--green-deep);
  box-shadow: 0 0 0 4px rgba(15, 138, 76, 0.12);
}

.reset-button {
  color: var(--muted);
}

.sorting-board {
  padding: 24px;
}

.source-lane,
.result-lane {
  border: 1px solid var(--line);
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.9);
}

.lane-header {
  min-height: 43px;
  padding: 0 15px;
  border-bottom: 1px solid var(--line);
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 9px;
  font-weight: 800;
  letter-spacing: 0.11em;
}

.count {
  display: inline-grid;
  place-items: center;
  min-width: 22px;
  height: 22px;
  border-radius: 999px;
  background: var(--paper);
  font-size: 10px;
}

.shape-grid {
  min-height: 150px;
  padding: 17px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
}

.data-card {
  min-width: 0;
  min-height: 106px;
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: 11px;
  background: var(--surface);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 8px;
  transition: transform 0.3s ease, opacity 0.3s ease, border-color 0.3s;
}

.data-card:hover {
  transform: translateY(-3px);
}

.data-card.moving {
  animation: card-pop 0.45s ease both;
}

@keyframes card-pop {
  0% { opacity: 0; transform: scale(0.82) translateY(-12px); }
  100% { opacity: 1; transform: scale(1) translateY(0); }
}

.shape {
  width: 42px;
  height: 42px;
  display: grid;
  place-items: center;
  color: #152019;
  font-size: 16px;
  font-weight: 800;
  filter: drop-shadow(3px 4px 0 rgba(23, 33, 27, 0.13));
}

.shape.circle {
  border-radius: 50%;
}

.shape.triangle {
  clip-path: polygon(50% 0, 100% 100%, 0 100%);
  padding-top: 13px;
}

.shape.hexagon {
  clip-path: polygon(25% 5%, 75% 5%, 100% 50%, 75% 95%, 25% 95%, 0 50%);
}

.shape.square {
  border-radius: 8px;
  transform: rotate(8deg);
}

.shape.orange { background: var(--orange); }
.shape.green { background: var(--green); }
.shape.blue { background: var(--blue); }
.shape.yellow { background: var(--yellow); }
.shape.pink { background: var(--pink); }

.data-card code {
  font-size: 10px;
  white-space: nowrap;
  overflow: hidden;
  max-width: 100%;
  text-overflow: ellipsis;
}

.result-lanes {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 13px;
  margin-top: 13px;
}

.result-dropzone {
  min-height: 203px;
  padding: 12px;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  align-content: start;
  gap: 9px;
}

.result-dropzone .data-card {
  min-height: 82px;
}

.result-dropzone .shape {
  width: 30px;
  height: 30px;
  font-size: 11px;
}

.match-lane {
  border-color: rgba(15, 138, 76, 0.28);
}

.no-match-lane {
  border-color: rgba(223, 78, 78, 0.2);
}

.status-icon {
  width: 18px;
  height: 18px;
  display: inline-grid;
  place-items: center;
  margin-right: 5px;
  border-radius: 50%;
  font-style: normal;
}

.status-icon.success {
  color: var(--green-deep);
  background: rgba(60, 255, 136, 0.2);
}

.status-icon.fail {
  color: #b53b3b;
  background: rgba(255, 117, 117, 0.15);
}

.empty-message {
  grid-column: 1 / -1;
  align-self: center;
  justify-self: center;
  color: #9aa19c;
  font-size: 10px;
  text-align: center;
}

.step-trace {
  margin: 18px 24px 0;
  padding: 15px;
  border: 1px solid rgba(15, 138, 76, 0.25);
  border-radius: 12px;
  background: rgba(241, 255, 246, 0.94);
}

.trace-header {
  display: flex;
  justify-content: space-between;
  font-size: 9px;
  font-weight: 800;
  letter-spacing: 0.11em;
}

.token-track {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  margin: 13px 0 10px;
}

.trace-token {
  padding: 7px 9px;
  border-radius: 7px;
  background: white;
  border: 1px solid var(--line);
  font-family: var(--mono);
  font-size: 11px;
}

.trace-token.active {
  color: #0c5d34;
  border-color: var(--green-deep);
  background: var(--green);
  transform: translateY(-2px);
}

.trace-token.done {
  opacity: 0.45;
}

#trace-message {
  margin: 0;
  color: var(--muted);
  font-size: 11px;
}

.hidden {
  display: none !important;
}

.concept-strip {
  max-width: 1400px;
  margin: 100px auto 120px;
}

.section-intro {
  display: grid;
  grid-template-columns: 0.8fr 1.2fr 0.8fr;
  gap: 30px;
  align-items: end;
  margin-bottom: 30px;
}

.section-intro .eyebrow {
  align-self: start;
}

.section-intro h2,
.content-heading h2 {
  margin: 0;
  font-size: clamp(30px, 4vw, 50px);
  letter-spacing: -0.05em;
  line-height: 1.05;
}

.section-intro > p:last-child,
.content-heading > p {
  color: var(--muted);
  line-height: 1.7;
  font-size: 13px;
  margin: 0;
}

.concept-cards {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  border-top: 1px solid var(--line);
  border-left: 1px solid var(--line);
}

.concept-card {
  min-height: 215px;
  padding: 25px;
  border: 0;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: transparent;
  text-align: left;
  cursor: pointer;
  transition: background 0.2s, transform 0.2s;
}

.concept-card:hover,
.concept-card.active {
  background: var(--surface);
  transform: translateY(-4px);
  box-shadow: var(--shadow);
}

.concept-symbol {
  display: block;
  margin-bottom: 45px;
  color: var(--green-deep);
  font-family: var(--mono);
  font-size: 27px;
  font-weight: 500;
}

.concept-card h3 {
  margin: 0 0 8px;
  font-size: 14px;
}

.concept-card p {
  margin: 0;
  color: var(--muted);
  font-size: 11px;
  line-height: 1.55;
}

.content-view {
  max-width: 1400px;
  margin: 0 auto;
  padding-bottom: 120px;
}

.content-heading {
  padding: 36px 0 42px;
  display: grid;
  grid-template-columns: 1.3fr 0.7fr;
  gap: 40px;
  align-items: end;
}

.lesson-layout {
  display: grid;
  grid-template-columns: 0.65fr 1.35fr;
  gap: 22px;
}

.lesson-list,
.lesson-detail,
.challenge-shell {
  border: 1px solid var(--line);
  border-radius: 18px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.route-picker {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 7px;
  margin-bottom: 14px;
}

.route-button {
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 11px 8px;
  background: var(--surface);
  color: var(--muted);
  cursor: pointer;
  font-size: 10px;
  font-weight: 700;
}

.route-button span {
  display: block;
  margin-bottom: 4px;
  color: var(--green-deep);
  font-family: var(--mono);
  font-size: 9px;
}

.route-button.active {
  background: var(--ink);
  border-color: var(--ink);
  color: var(--surface);
}

.lesson-list {
  padding: 10px;
  max-height: 720px;
  overflow-y: auto;
  scrollbar-width: thin;
  scrollbar-color: var(--line) transparent;
}

.lesson-button {
  width: 100%;
  border: 0;
  background: transparent;
  padding: 16px;
  border-radius: 12px;
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 13px;
  align-items: center;
  text-align: left;
  cursor: pointer;
}

.lesson-button:hover,
.lesson-button.active {
  background: var(--paper);
}

.lesson-index {
  color: var(--green-deep);
  font-family: var(--mono);
  font-size: 11px;
}

.lesson-button strong {
  font-size: 13px;
}

.lesson-button small {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  font-size: 10px;
}

.complete-mark {
  color: var(--green-deep);
}

.lesson-detail {
  min-height: 520px;
  padding: clamp(28px, 4vw, 55px);
}

.lesson-kicker {
  color: var(--green-deep);
  font-size: 10px;
  font-weight: 800;
  letter-spacing: 0.12em;
}

.lesson-detail h3 {
  margin: 12px 0 16px;
  font-size: 32px;
  letter-spacing: -0.04em;
}

.lesson-detail > p {
  color: var(--muted);
  line-height: 1.75;
  max-width: 690px;
}

.lesson-demo {
  margin: 28px 0;
  padding: 22px;
  border-radius: 14px;
  background: #151f19;
  color: white;
}

.lesson-demo code {
  display: block;
  color: var(--green);
  font-size: 20px;
  margin-bottom: 13px;
}

.lesson-demo p {
  margin: 0;
  color: #b8c0ba;
  font-size: 12px;
  line-height: 1.6;
}

.lesson-actions {
  display: flex;
  gap: 10px;
}

.challenge-shell {
  display: grid;
  grid-template-columns: 0.8fr 1.2fr;
  overflow: hidden;
}

.challenge-copy {
  padding: clamp(28px, 5vw, 60px);
  background: var(--ink);
  color: white;
}

.challenge-tag {
  color: var(--green);
  font-size: 10px;
  font-weight: 800;
  letter-spacing: 0.13em;
}

.challenge-copy h3 {
  font-size: 34px;
  line-height: 1.1;
  letter-spacing: -0.04em;
  margin: 18px 0;
}

.challenge-copy > p {
  color: #b9c2bc;
  font-size: 13px;
  line-height: 1.75;
}

.challenge-example {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 15px;
  margin-top: 14px;
  padding: 13px 15px;
  border: 1px solid rgba(60, 255, 136, 0.28);
  border-radius: 10px;
}

.challenge-example.reject {
  border-color: rgba(255, 117, 151, 0.28);
}

.challenge-example span {
  color: #aab5ae;
  font-size: 10px;
}

.challenge-example code {
  color: var(--green);
}

.challenge-example.reject code {
  color: var(--pink);
}

.challenge-hint {
  margin-top: 20px;
  color: var(--green);
}

.hint {
  padding: 12px;
  border-left: 2px solid var(--green);
  background: rgba(60, 255, 136, 0.08);
}

.challenge-test-panel {
  padding: clamp(28px, 5vw, 60px);
}

.regex-input-wrap.large {
  margin-bottom: 26px;
}

.test-cases {
  display: grid;
  gap: 8px;
  margin-bottom: 25px;
}

.test-case {
  display: grid;
  grid-template-columns: 1fr auto auto;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 9px;
}

.test-case code {
  font-size: 12px;
}

.expectation {
  color: var(--muted);
  font-size: 9px;
  text-transform: uppercase;
}

.test-result {
  width: 21px;
  height: 21px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--paper);
  font-size: 11px;
}

.test-case.pass .test-result {
  background: rgba(60, 255, 136, 0.2);
  color: var(--green-deep);
}

.test-case.fail .test-result {
  background: rgba(255, 117, 151, 0.15);
  color: #b53b3b;
}

.full-width {
  width: 100%;
}

.challenge-feedback {
  min-height: 20px;
  margin: 16px 0 0;
  text-align: center;
  color: var(--muted);
  font-size: 12px;
}

.tool-nav {
  display: flex;
  gap: 6px;
  padding: 6px;
  margin-bottom: 18px;
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--surface);
}

.tool-tab {
  flex: 1 0 auto;
  border: 0;
  border-radius: 9px;
  padding: 11px 15px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  font-size: 11px;
  font-weight: 800;
}

.tool-tab.active {
  background: var(--ink);
  color: var(--surface);
}

.tool-panel {
  display: none;
  grid-template-columns: minmax(330px, 0.85fr) minmax(420px, 1.15fr);
  overflow: hidden;
  min-height: 590px;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.tool-panel.active {
  display: grid;
  animation: reveal 0.25s ease both;
}

.tool-copy,
.tool-output {
  padding: clamp(25px, 4vw, 48px);
}

.tool-copy {
  border-right: 1px solid var(--line);
}

.tool-output {
  background:
    linear-gradient(rgba(23, 33, 27, 0.027) 1px, transparent 1px),
    linear-gradient(90deg, rgba(23, 33, 27, 0.027) 1px, transparent 1px),
    color-mix(in srgb, var(--paper) 70%, var(--surface));
  background-size: 28px 28px;
}

.tool-number,
.output-label {
  color: var(--green-deep);
  font-size: 9px;
  font-weight: 800;
  letter-spacing: 0.14em;
}

.tool-copy h3,
.reference-grid h3,
.teacher-panel h3 {
  margin: 13px 0;
  font-size: 26px;
  letter-spacing: -0.04em;
}

.tool-copy > p,
.reference-grid p,
.teacher-panel p {
  color: var(--muted);
  font-size: 12px;
  line-height: 1.75;
}

.tool-copy label,
.engine-patterns label,
.inline-fields label {
  display: grid;
  gap: 7px;
  margin: 17px 0;
  color: var(--muted);
  font-size: 9px;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.tool-copy input,
.tool-copy textarea,
.case-row input {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 12px 13px;
  outline: none;
  background: var(--surface);
  color: var(--ink);
  font-family: var(--mono);
  font-size: 12px;
  resize: vertical;
}

.tool-copy input:focus,
.tool-copy textarea:focus,
.case-row input:focus {
  border-color: var(--green-deep);
  box-shadow: 0 0 0 3px rgba(60, 255, 136, 0.13);
}

.inline-fields,
.engine-patterns {
  display: grid;
  grid-template-columns: 1fr 72px;
  gap: 10px;
}

.engine-patterns {
  grid-template-columns: 1fr 1fr;
}

.highlight-output,
.replace-output {
  min-height: 170px;
  margin-top: 17px;
  padding: 22px;
  border: 1px solid var(--line);
  border-radius: 13px;
  background: var(--surface);
  color: var(--ink);
  white-space: pre-wrap;
  overflow-wrap: anywhere;
  font-family: var(--mono);
  font-size: 14px;
  line-height: 2;
}

.match-highlight {
  padding: 3px 1px;
  border-bottom: 3px solid var(--green-deep);
  background: rgba(60, 255, 136, 0.2);
  border-radius: 3px;
}

.capture-list {
  display: grid;
  gap: 8px;
  margin-top: 18px;
}

.capture-item,
.replacement-map-item {
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 9px;
  background: var(--surface);
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 10px;
  align-items: center;
  font-size: 10px;
}

.capture-color {
  width: 9px;
  height: 9px;
  border-radius: 50%;
}

.capture-item code {
  justify-self: end;
}

.replacement-map {
  display: grid;
  gap: 8px;
  margin-top: 18px;
}

.case-editor {
  display: grid;
  gap: 8px;
}

.case-row {
  display: grid;
  grid-template-columns: 1fr 105px 34px;
  gap: 7px;
}

.case-row select,
.case-delete {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  font-size: 10px;
}

.case-delete {
  cursor: pointer;
}

.case-actions,
.export-actions {
  display: flex;
  gap: 9px;
  margin-top: 18px;
  flex-wrap: wrap;
}

.score-ring {
  width: 150px;
  height: 150px;
  margin: 28px auto;
  border: 10px solid var(--line);
  border-radius: 50%;
  display: grid;
  place-content: center;
  text-align: center;
}

.score-ring strong {
  font-family: var(--mono);
  font-size: 28px;
}

.score-ring span {
  color: var(--muted);
  font-size: 9px;
}

.case-report {
  display: grid;
  gap: 7px;
}

.case-report-row {
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  display: flex;
  justify-content: space-between;
  background: var(--surface);
  font-size: 10px;
}

.case-report-row.pass { border-left: 3px solid var(--green-deep); }
.case-report-row.fail { border-left: 3px solid var(--pink); }

.file-button {
  position: relative;
}

.file-button input {
  position: absolute;
  inset: 0;
  opacity: 0;
  cursor: pointer;
}

.comparison-result {
  margin-bottom: 17px;
}

.comparison-result > div {
  min-height: 62px;
  margin-top: 8px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 9px;
  background: var(--surface);
  font-family: var(--mono);
  font-size: 11px;
  line-height: 1.8;
}

.engine-trace {
  margin-top: 25px;
  padding: 18px;
  border-radius: 12px;
  background: var(--surface);
  border: 1px solid var(--line);
}

.engine-cells {
  display: flex;
  gap: 5px;
  margin: 18px 0;
  flex-wrap: wrap;
}

.engine-cell {
  width: 30px;
  height: 34px;
  display: grid;
  place-items: center;
  border: 1px solid var(--line);
  border-radius: 6px;
  font-family: var(--mono);
  font-size: 11px;
}

.engine-cell.active {
  background: var(--green);
  border-color: var(--green-deep);
  color: #101612;
}

.engine-cell.backtrack {
  background: var(--yellow);
  color: #101612;
}

#engine-message {
  min-height: 34px;
  color: var(--muted);
  font-size: 11px;
}

.performance-meter {
  height: 6px;
  overflow: hidden;
  border-radius: 999px;
  background: var(--line);
}

.performance-meter span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--green-deep);
  transition: width 0.3s;
}

.security-warning {
  padding: 10px 12px;
  border-left: 3px solid var(--orange);
  background: rgba(255, 124, 69, 0.1);
  color: var(--muted);
  font-size: 10px;
}

.speed-control {
  margin-top: 20px;
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 10px;
  color: var(--muted);
  font-size: 9px;
}

.block-palette {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin: 24px 0 15px;
}

.block-button {
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 12px;
  background: var(--surface);
  cursor: pointer;
  text-align: left;
}

.block-button code {
  display: block;
  color: var(--green-deep);
  font-size: 13px;
}

.block-button span {
  display: block;
  margin-top: 5px;
  color: var(--muted);
  font-size: 9px;
}

.builder-track {
  min-height: 135px;
  margin: 15px 0 25px;
  padding: 14px;
  border: 1px dashed var(--line);
  border-radius: 12px;
  display: flex;
  align-content: flex-start;
  flex-wrap: wrap;
  gap: 8px;
}

.builder-block {
  border: 1px solid var(--green-deep);
  border-radius: 7px;
  padding: 9px 11px;
  background: rgba(60, 255, 136, 0.11);
  cursor: pointer;
  font-family: var(--mono);
  font-size: 10px;
}

.generated-regex {
  margin: 12px 0;
  padding: 17px;
  border-radius: 10px;
  background: var(--ink);
  color: var(--green);
  overflow-wrap: anywhere;
  font-family: var(--mono);
}

#builder-explanation {
  color: var(--muted);
  min-height: 42px;
  font-size: 11px;
  line-height: 1.6;
}

.reference-grid {
  grid-column: 1 / -1;
  padding: clamp(24px, 4vw, 48px);
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 16px;
}

.reference-grid article {
  padding: 24px;
  border: 1px solid var(--line);
  border-radius: 13px;
  background: color-mix(in srgb, var(--paper) 55%, var(--surface));
}

.flag-list,
.engine-table {
  display: grid;
  gap: 7px;
}

.flag-row,
.engine-row {
  padding: 9px 11px;
  border-bottom: 1px solid var(--line);
  display: grid;
  grid-template-columns: 30px 1fr;
  gap: 10px;
  font-size: 10px;
}

.flag-row code {
  color: var(--green-deep);
}

.reference-example {
  width: 100%;
  margin-top: 8px;
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 12px;
  background: var(--surface);
  color: var(--ink);
  display: grid;
  gap: 5px;
  text-align: left;
  cursor: pointer;
}

.reference-example code { color: var(--green-deep); }
.reference-example span { color: var(--muted); font-size: 9px; }

.danger-example,
.safe-example {
  margin-top: 9px;
  padding: 12px;
  border-radius: 9px;
  display: flex;
  justify-content: space-between;
  gap: 10px;
  font-size: 9px;
}

.danger-example { background: rgba(255, 117, 151, 0.12); }
.safe-example { background: rgba(60, 255, 136, 0.12); }

.teacher-panel {
  margin-top: 22px;
  padding: 28px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 20px;
  align-items: center;
}

.teacher-panel h3,
.teacher-panel p {
  margin-top: 4px;
  margin-bottom: 4px;
}

.teacher-actions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.share-status {
  grid-column: 1 / -1;
  color: var(--green-deep) !important;
  text-align: right;
}

body.teacher-mode .expectation,
body.teacher-mode .challenge-example,
body.teacher-mode .challenge-hint,
body.teacher-mode .hint {
  visibility: hidden;
}

body.no-motion *,
body.no-motion *::before,
body.no-motion *::after {
  animation: none !important;
  transition: none !important;
  scroll-behavior: auto !important;
}

body.presentation-mode .topbar,
body.presentation-mode footer,
body.presentation-mode .teacher-panel {
  display: none;
}

body.presentation-mode main {
  padding-top: 30px;
}

footer {
  padding: 28px clamp(24px, 5vw, 76px);
  border-top: 1px solid var(--line);
  display: flex;
  justify-content: space-between;
  color: var(--muted);
  font-size: 11px;
}

body.dark {
  color-scheme: dark;
  --ink: #edf5ef;
  --muted: #a1aba4;
  --paper: #101612;
  --surface: #17201a;
  --line: #2b362f;
  --green-deep: #49e78b;
  --shadow: 0 18px 50px rgba(0, 0, 0, 0.25);
  background: radial-gradient(circle at 85% 2%, rgba(60, 255, 136, 0.08), transparent 23rem), var(--paper);
}

body.dark .topbar {
  background: rgba(16, 22, 18, 0.87);
}

body.dark .brand-mark {
  background: #edf5ef;
  color: #0f6b3a;
}

body.dark .regex-input-wrap,
body.dark .visual-stage {
  background-color: #121a15;
}

body.dark .stage-topbar {
  background: rgba(23, 32, 26, 0.85);
}

body.dark .explanation-card,
body.dark .step-trace {
  background: rgba(60, 255, 136, 0.07);
}

body.dark .trace-token {
  background: var(--surface);
}

body.dark .button.primary {
  background: var(--green);
  border-color: var(--green);
  color: #101612;
  box-shadow: 4px 4px 0 #edf5ef;
}

body.dark .button.primary:hover {
  box-shadow: 6px 6px 0 #edf5ef;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

@media (max-width: 1000px) {
  .hero {
    grid-template-columns: 1fr;
    gap: 24px;
  }

  .workspace {
    grid-template-columns: 1fr;
  }

  .control-panel {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .section-intro {
    grid-template-columns: 1fr 1fr;
  }

  .section-intro .eyebrow {
    grid-column: 1 / -1;
  }

  .concept-cards {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 760px) {
  .topbar {
    height: auto;
    min-height: 70px;
    grid-template-columns: 1fr auto;
    padding-top: 12px;
    padding-bottom: 12px;
  }

  .main-nav {
    grid-column: 1 / -1;
    grid-row: 2;
    width: 100%;
    margin-top: 12px;
  }

  .nav-link {
    flex: 1;
  }

  .progress-pill {
    display: none;
  }

  .hero {
    padding-top: 54px;
  }

  .hero h1 {
    font-size: clamp(43px, 14vw, 68px);
  }

  .control-panel {
    padding: 24px 18px;
  }

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

  .result-lanes,
  .challenge-shell,
  .content-heading,
  .lesson-layout {
    grid-template-columns: 1fr;
  }

  .result-dropzone {
    min-height: 145px;
  }

  .section-intro,
  .concept-cards {
    grid-template-columns: 1fr;
  }

  .section-intro .eyebrow {
    grid-column: auto;
  }

  .concept-card {
    min-height: 170px;
  }

  .concept-symbol {
    margin-bottom: 25px;
  }

  .run-actions {
    grid-template-columns: 1fr;
  }

  .tool-panel,
  .reference-grid,
  .teacher-panel {
    grid-template-columns: 1fr;
  }

  .tool-copy {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .inline-fields,
  .engine-patterns {
    grid-template-columns: 1fr;
  }

  .case-row {
    grid-template-columns: 1fr 95px 34px;
  }

  .teacher-actions {
    justify-content: flex-start;
  }

  .route-picker {
    grid-template-columns: repeat(2, 1fr);
  }

  footer {
    gap: 10px;
    flex-direction: column;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}