:root {
  --page: #f4f6f3;
  --surface: #ffffff;
  --surface-2: #eef3ef;
  --ink: #17201b;
  --muted: #5c6862;
  --quiet: #7a8580;
  --line: #d7ded8;
  --line-dark: #aab6af;
  --green: #1f6b4c;
  --green-dark: #153d31;
  --pine: #9f3e34;
  --hardwood: #2f6f8d;
  --gold: #d99a28;
  --violet: #6f5b9a;
  --danger: #a43f35;
  --ok: #24724f;
  --shadow: 0 12px 32px rgba(30, 44, 36, .08);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: var(--ink);
  background: var(--page);
}

* { box-sizing: border-box; }

html { min-width: 320px; overflow-x: hidden; scroll-behavior: smooth; }

body {
  min-height: 100vh;
  margin: 0;
  overflow-x: hidden;
  background: var(--page);
}

button,
input,
select {
  font: inherit;
}

button,
select {
  cursor: pointer;
}

.skip-link {
  position: fixed;
  left: 16px;
  top: -70px;
  z-index: 20;
  padding: 10px 14px;
  background: var(--ink);
  color: #fff;
}

.skip-link:focus { top: 14px; }

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 22px;
  min-height: 78px;
  padding: 16px 26px;
  border-bottom: 1px solid var(--line);
  background: var(--surface);
}

.brand-block {
  display: flex;
  align-items: center;
  gap: 13px;
  min-width: 0;
}

.course-mark {
  display: grid;
  place-items: center;
  width: 44px;
  height: 44px;
  flex: 0 0 auto;
  background: var(--green-dark);
  color: #fff;
  font-family: Georgia, "Times New Roman", serif;
  font-weight: 800;
}

.eyebrow,
.nav-label,
.case-picker span {
  margin: 0 0 4px;
  color: var(--green);
  font-size: 11px;
  font-weight: 850;
  letter-spacing: .08em;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 0;
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(23px, 2.4vw, 32px);
  line-height: 1.05;
}

h2 {
  margin-bottom: 12px;
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(29px, 3.6vw, 47px);
  line-height: 1.07;
}

h3 {
  margin-bottom: 7px;
  font-size: 18px;
  line-height: 1.2;
}

.lead {
  max-width: 780px;
  margin-bottom: 0;
  color: #46534d;
  font-size: 16px;
  line-height: 1.6;
}

.case-picker {
  display: grid;
  min-width: min(340px, 45vw);
}

.case-picker select {
  width: 100%;
  min-height: 42px;
  padding: 0 38px 0 12px;
  border: 1px solid var(--line-dark);
  border-radius: 4px;
  background: #fff;
  color: var(--ink);
}

.app-layout {
  display: grid;
  grid-template-columns: 220px minmax(550px, 1fr) 360px;
  min-height: calc(100vh - 78px);
}

.lesson-nav,
.control-room {
  background: var(--surface);
}

.lesson-nav {
  padding: 28px 17px;
  border-right: 1px solid var(--line);
}

.nav-label {
  padding-left: 10px;
  margin-bottom: 13px;
}

#stepNav {
  display: grid;
  gap: 5px;
}

.nav-button {
  display: grid;
  grid-template-columns: 29px 1fr;
  align-items: start;
  gap: 8px;
  width: 100%;
  padding: 11px 9px;
  border: 0;
  border-left: 3px solid transparent;
  background: transparent;
  color: var(--muted);
  text-align: left;
}

.nav-button:hover {
  background: var(--surface-2);
  color: var(--ink);
}

.nav-button.active {
  border-left-color: var(--green);
  background: #e5f0e9;
  color: var(--green-dark);
  font-weight: 780;
}

.nav-index {
  color: var(--quiet);
  font-size: 12px;
  font-variant-numeric: tabular-nums;
}

.case-facts {
  margin: 28px 9px 0;
  padding-top: 18px;
  border-top: 1px solid var(--line);
}

.fact-row {
  display: grid;
  gap: 3px;
  padding: 10px 0;
  border-bottom: 1px solid #edf1ed;
}

.fact-row span {
  color: var(--quiet);
  font-size: 10px;
  font-weight: 800;
  letter-spacing: .05em;
  text-transform: uppercase;
}

.fact-row strong {
  color: var(--green-dark);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 19px;
  line-height: 1.2;
}

.stage {
  min-width: 0;
  padding: clamp(22px, 3vw, 38px);
  overflow: hidden;
}

.stage-header {
  display: flex;
  justify-content: space-between;
  gap: 22px;
  width: min(100%, 1140px);
  max-width: 1140px;
  margin: 0 auto 22px;
  min-width: 0;
}

.stage-header > div:first-child {
  min-width: 0;
}

.stage-header h2,
.lead {
  overflow-wrap: anywhere;
}

.status-chip {
  align-self: flex-start;
  min-width: 152px;
  padding: 11px 13px;
  border: 1px solid var(--line);
  border-left: 4px solid var(--gold);
  background: var(--surface);
  color: var(--muted);
  font-size: 12px;
  line-height: 1.4;
  box-shadow: var(--shadow);
}

.status-chip strong {
  display: block;
  color: var(--ink);
  font-size: 18px;
  font-variant-numeric: tabular-nums;
}

.graph-shell,
.lesson-panel,
.calculation-panel,
.control-section {
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.graph-shell {
  width: min(100%, 1140px);
  max-width: 1140px;
  margin: 0 auto;
  overflow: hidden;
}

.graph-title-row {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 16px;
  padding: 18px 20px 12px;
  border-bottom: 1px solid var(--line);
}

.graph-title-row h3 {
  margin-bottom: 0;
  font-family: Georgia, "Times New Roman", serif;
  font-size: 22px;
}

.secondary-button,
.primary-button,
.small-button,
.toggle-button,
.constraint-button,
.vertex-button {
  border: 1px solid var(--line-dark);
  border-radius: 4px;
  background: #fff;
  color: var(--ink);
  font-weight: 780;
}

.secondary-button {
  min-height: 38px;
  padding: 0 13px;
  white-space: nowrap;
}

.secondary-button:hover,
.small-button:hover,
.toggle-button:hover {
  border-color: var(--green);
}

.graph-canvas {
  width: 100%;
  min-height: 470px;
  padding: 10px 14px 14px;
}

.graph-canvas svg {
  display: block;
  width: 100%;
  height: auto;
}

.axis-line {
  stroke: #1f2924;
  stroke-width: 1.5;
}

.grid-line {
  stroke: #e5ebe6;
  stroke-width: 1;
}

.axis-label,
.tick-label,
.constraint-label,
.objective-label,
.point-label {
  font-family: Inter, ui-sans-serif, system-ui, sans-serif;
}

.axis-label {
  fill: #25332c;
  font-size: 13px;
  font-weight: 780;
}

.tick-label {
  fill: #77837d;
  font-size: 11px;
}

.constraint-line {
  fill: none;
  stroke-width: 2.4;
}

.constraint-line.muted {
  opacity: .46;
}

.constraint-line.selected {
  stroke-width: 3.4;
  opacity: 1;
}

.constraint-label {
  fill: #36423c;
  font-size: 12px;
  font-weight: 760;
}

.feasible-region {
  fill: rgba(31, 107, 76, .18);
  stroke: rgba(31, 107, 76, .78);
  stroke-width: 2;
}

.half-plane {
  opacity: .11;
}

.objective-line {
  fill: none;
  stroke: #151b18;
  stroke-width: 2.2;
  stroke-dasharray: 8 6;
}

.objective-arrow {
  stroke: #151b18;
  stroke-width: 2;
}

.objective-label {
  fill: #151b18;
  font-size: 12px;
  font-weight: 820;
}

.vertex-point {
  fill: #fff;
  stroke: var(--green-dark);
  stroke-width: 2;
}

.vertex-point.optimum {
  fill: var(--gold);
  stroke: #5c3b00;
  stroke-width: 2.4;
}

.probe-point {
  stroke: #222;
  stroke-width: 2;
}

.point-label {
  fill: #26342e;
  font-size: 11px;
  font-weight: 760;
}

.teaching-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.12fr) minmax(320px, .88fr);
  gap: 16px;
  width: min(100%, 1140px);
  max-width: 1140px;
  margin: 16px auto 0;
}

.lesson-panel,
.calculation-panel {
  min-width: 0;
  padding: 20px;
}

.lesson-panel h3,
.calculation-panel h3,
.control-section h3 {
  font-family: Georgia, "Times New Roman", serif;
  font-size: 21px;
}

.lesson-panel p,
.calculation-panel p,
.control-section p,
.source-sketch figcaption {
  color: var(--muted);
  font-size: 13px;
  line-height: 1.55;
}

.concept-list {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-top: 16px;
}

.concept-item {
  min-width: 0;
  padding: 14px;
  border-top: 4px solid var(--green);
  background: var(--surface-2);
}

.concept-item:nth-child(2) { border-top-color: var(--hardwood); }
.concept-item:nth-child(3) { border-top-color: var(--gold); }

.concept-item strong {
  display: block;
  margin-bottom: 5px;
  font-size: 14px;
}

.concept-item span {
  color: var(--muted);
  font-size: 12px;
  line-height: 1.45;
}

.equation-card {
  margin-top: 16px;
  padding: 15px;
  border-left: 4px solid var(--gold);
  background: #fff8e9;
}

.equation-card code,
.math-line,
.matrix-cell code,
.slack-table code {
  font-family: "Segoe UI Symbol", "Cambria Math", Georgia, serif;
}

.equation-card code {
  display: block;
  color: #50370b;
  font-size: 20px;
  line-height: 1.45;
  white-space: normal;
}

.constraint-list {
  display: grid;
  gap: 8px;
  margin-top: 14px;
}

.constraint-pill {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  background: #fbfcfb;
}

.constraint-pill span {
  min-width: 0;
  color: var(--muted);
  font-size: 12px;
}

.constraint-pill code {
  color: var(--ink);
  text-align: right;
  white-space: normal;
}

.table-wrap {
  width: 100%;
  margin-top: 13px;
  overflow-x: auto;
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 12px;
}

th,
td {
  padding: 9px 8px;
  border-bottom: 1px solid var(--line);
  text-align: right;
  vertical-align: top;
}

th:first-child,
td:first-child {
  text-align: left;
}

thead th {
  color: var(--quiet);
  font-size: 10px;
  font-weight: 850;
  letter-spacing: .05em;
  text-transform: uppercase;
}

tbody tr.optimum-row {
  background: #fff5d9;
}

.vertex-button {
  min-height: 26px;
  padding: 3px 7px;
  border-color: #d6c07e;
  background: #fffaf0;
  color: #533b08;
  font-size: 11px;
}

.slack-table .binding {
  color: var(--gold);
  font-weight: 850;
}

.slack-table .clear {
  color: var(--ok);
  font-weight: 800;
}

.control-room {
  padding: 24px 18px;
  border-left: 1px solid var(--line);
  overflow: hidden;
}

.control-section {
  padding: 17px;
}

.control-section + .control-section {
  margin-top: 14px;
}

.control-section h3 {
  margin-bottom: 10px;
}

.objective-readout {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: end;
  gap: 12px;
  margin-bottom: 11px;
}

.objective-readout strong {
  color: var(--green-dark);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 26px;
  font-variant-numeric: tabular-nums;
}

.range-row input[type="range"] {
  width: 100%;
  accent-color: var(--green);
}

.button-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin-top: 12px;
}

.small-button,
.primary-button,
.toggle-button {
  min-height: 37px;
  padding: 0 10px;
}

.primary-button {
  border-color: var(--green);
  background: var(--green);
  color: #fff;
}

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

.constraint-buttons {
  display: grid;
  gap: 7px;
}

.constraint-button {
  display: grid;
  grid-template-columns: 12px 1fr;
  gap: 9px;
  align-items: center;
  width: 100%;
  padding: 9px;
  text-align: left;
}

.constraint-button .swatch {
  width: 12px;
  height: 12px;
  border-radius: 50%;
}

.constraint-button.active {
  border-color: var(--green);
  background: #edf6ef;
}

.constraint-button code {
  display: block;
  color: var(--ink);
  font-size: 12px;
  white-space: normal;
}

.constraint-meta {
  margin-top: 13px;
  padding-top: 12px;
  border-top: 1px solid var(--line);
}

.constraint-meta dl {
  display: grid;
  grid-template-columns: 78px 1fr;
  gap: 6px 10px;
  margin: 0;
  font-size: 12px;
}

.constraint-meta dt {
  color: var(--quiet);
}

.constraint-meta dd {
  margin: 0;
  color: var(--ink);
}

details.editor-details summary {
  color: var(--green-dark);
  font-weight: 850;
  cursor: pointer;
}

.editor-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
  margin-top: 13px;
}

.editor-field {
  display: grid;
  gap: 5px;
}

.editor-field label,
.constraint-editor label {
  color: var(--quiet);
  font-size: 10px;
  font-weight: 820;
  letter-spacing: .05em;
  text-transform: uppercase;
}

.editor-field input,
.editor-field select,
.constraint-editor input,
.constraint-editor select,
.probe-form input {
  width: 100%;
  min-height: 34px;
  padding: 6px 8px;
  border: 1px solid var(--line-dark);
  border-radius: 4px;
  background: #fff;
  color: var(--ink);
}

.constraint-editor {
  margin-top: 14px;
}

.constraint-editor .table-wrap {
  margin-top: 8px;
}

.constraint-editor th,
.constraint-editor td {
  padding: 5px 4px;
}

.constraint-editor input,
.constraint-editor select {
  min-width: 62px;
  font-size: 12px;
}

.constraint-editor input[data-field="label"] {
  min-width: 112px;
}

.probe-form {
  display: grid;
  grid-template-columns: 1fr 1fr auto;
  gap: 8px;
  align-items: end;
  margin-top: 13px;
}

.probe-result {
  margin-top: 12px;
  padding: 12px;
  border-left: 4px solid var(--line-dark);
  background: #f8faf8;
  font-size: 12px;
  line-height: 1.5;
}

.probe-result.pass {
  border-left-color: var(--ok);
}

.probe-result.fail {
  border-left-color: var(--danger);
}

.source-sketch {
  display: none;
}

.source-sketch.visible {
  display: block;
}

.source-sketch figure {
  margin: 0;
}

.source-sketch img {
  display: block;
  width: 100%;
  height: auto;
  border: 1px solid var(--line);
  background: #fff;
}

.source-sketch figcaption {
  margin-top: 8px;
  margin-bottom: 0;
}

.model-note {
  margin: 13px 0 0;
  color: var(--quiet);
  font-size: 12px;
  line-height: 1.45;
}

.active-list {
  display: grid;
  gap: 7px;
  margin-top: 12px;
}

.active-list code {
  display: block;
  padding: 9px 10px;
  border-left: 4px solid var(--gold);
  background: #fff8e9;
  color: #4d350a;
  white-space: normal;
}

.matrix {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
  margin-top: 14px;
}

.matrix-cell {
  padding: 13px;
  border: 1px solid var(--line);
  background: #fbfcfb;
}

.matrix-cell span {
  display: block;
  margin-bottom: 4px;
  color: var(--quiet);
  font-size: 10px;
  font-weight: 820;
  letter-spacing: .05em;
  text-transform: uppercase;
}

.matrix-cell code {
  color: var(--ink);
  font-size: 16px;
  white-space: normal;
}

@media (max-width: 1240px) {
  .app-layout {
    grid-template-columns: 190px minmax(500px, 1fr);
  }

  .control-room {
    grid-column: 1 / -1;
    border-top: 1px solid var(--line);
    border-left: 0;
  }

  .control-room {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 14px;
  }

  .control-section + .control-section {
    margin-top: 0;
  }

  .source-sketch.visible {
    display: block;
  }
}

@media (max-width: 860px) {
  .topbar {
    display: block;
    padding: 15px 16px;
  }

  .case-picker {
    min-width: 0;
    margin-top: 13px;
  }

  .app-layout {
    display: block;
  }

  .lesson-nav {
    position: sticky;
    top: 0;
    z-index: 10;
    width: 100vw;
    max-width: 100vw;
    padding: 8px;
    border-right: 0;
    border-bottom: 1px solid var(--line);
    overflow-x: auto;
  }

  .nav-label,
  .case-facts {
    display: none;
  }

  #stepNav {
    display: flex;
    width: max-content;
  }

  .nav-button {
    grid-template-columns: auto auto;
    width: auto;
    min-width: 126px;
    padding: 9px 10px;
    border-left: 0;
    border-bottom: 3px solid transparent;
  }

  .nav-button.active {
    border-left-color: transparent;
    border-bottom-color: var(--green);
  }

  .stage {
    width: 100vw;
    max-width: 100vw;
    padding: 22px 14px;
  }

  .stage-header,
  .graph-shell,
  .teaching-grid {
    width: calc(100vw - 28px);
    max-width: calc(100vw - 28px);
  }

  .stage-header,
  .graph-title-row {
    display: block;
  }

  .status-chip,
  .secondary-button {
    margin-top: 13px;
  }

  .graph-canvas {
    min-height: 300px;
    padding: 6px;
    width: 100%;
    max-width: 100%;
  }

  .constraint-label,
  .objective-label,
  .point-label {
    font-size: 10px;
  }

  .teaching-grid,
  .concept-list,
  .matrix {
    grid-template-columns: 1fr;
  }

  .control-room {
    display: block;
    width: 100vw;
    max-width: 100vw;
    padding: 18px 14px;
  }

  .control-section + .control-section {
    margin-top: 14px;
  }

  .probe-form {
    grid-template-columns: 1fr 1fr;
  }

  .probe-form button {
    grid-column: 1 / -1;
  }
}

@media (max-width: 520px) {
  h2 {
    font-size: 31px;
  }

  .button-row,
  .editor-grid {
    grid-template-columns: 1fr;
  }

  .objective-readout {
    grid-template-columns: 1fr;
  }

  .graph-canvas {
    overflow-x: visible;
  }

  .graph-canvas svg {
    min-width: 0;
  }

  footer {
    display: block;
  }

  footer span {
    display: block;
    margin: 4px 0;
  }
}

footer {
  display: flex;
  justify-content: space-between;
  gap: 18px;
  padding: 14px 24px;
  border-top: 1px solid var(--line);
  background: var(--surface);
  color: var(--quiet);
  font-size: 11px;
}

@media (max-width: 520px) {
  footer {
    display: block;
  }

  footer span {
    display: block;
    margin: 4px 0;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition: none !important;
  }
}