:root {
  color-scheme: light;
  --ink: #1f2528;
  --muted: #5d676b;
  --subtle: #eff2f1;
  --line: #d7ddda;
  --paper: #fbfcfb;
  --panel: #ffffff;
  --accent: #2f5d50;
  --accent-soft: #e3eee9;
  --focus: #8a5a2b;
  --shadow: 0 1px 2px rgba(31, 37, 40, 0.08);
  font-family: "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

[data-theme="dark"] {
  color-scheme: dark;
  --ink: #edf1ef;
  --muted: #aeb9b5;
  --subtle: #1d2422;
  --line: #34413d;
  --paper: #101513;
  --panel: #171e1b;
  --accent: #8dc6b3;
  --accent-soft: #1f332d;
  --focus: #d0a06c;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.36);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-size: 16px;
  line-height: 1.6;
}

a {
  color: inherit;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--paper) 96%, transparent);
  backdrop-filter: blur(10px);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
  min-height: 64px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 650;
  text-decoration: none;
}

.brand-mark {
  display: inline-grid;
  place-items: center;
  width: 32px;
  height: 32px;
  border: 1px solid var(--accent);
  color: var(--accent);
  font-family: Georgia, "Times New Roman", serif;
}

nav {
  display: flex;
  gap: 18px;
  color: var(--muted);
  font-size: 0.94rem;
}

nav a {
  text-decoration: none;
}

nav a:hover,
.toc a:hover {
  color: var(--accent);
}

nav a[aria-current="page"] {
  color: var(--accent);
  font-weight: 700;
}

.theme-toggle {
  display: inline-flex;
  align-items: center;
  min-height: 38px;
  border: 1px solid var(--line);
  background: var(--panel);
  color: var(--ink);
  padding: 0 12px;
  font: inherit;
  font-size: 0.9rem;
  cursor: pointer;
  white-space: nowrap;
}

.theme-toggle:hover {
  border-color: var(--accent);
  color: var(--accent);
}

main {
  padding-bottom: 56px;
}

.intro-section {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 360px;
  gap: 48px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
  padding: 56px 0 36px;
}

.intro-single {
  grid-template-columns: 1fr;
  max-width: 980px;
}

.kicker {
  margin: 0 0 12px;
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

h1,
h2,
h3 {
  margin: 0;
  line-height: 1.18;
  letter-spacing: 0;
}

h1 {
  max-width: 780px;
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(2.4rem, 5vw, 4.8rem);
  font-weight: 500;
}

h2 {
  font-family: Georgia, "Times New Roman", serif;
  font-size: 2rem;
  font-weight: 500;
}

h3 {
  font-size: 1.22rem;
  font-weight: 650;
}

.lede {
  max-width: 790px;
  margin-top: 24px;
  color: color-mix(in srgb, var(--ink) 82%, var(--muted));
  font-size: 1.17rem;
}

.byline {
  margin: 18px 0 0;
  color: var(--muted);
  font-size: 0.98rem;
  font-weight: 650;
}

.intro-copy p:not(.kicker, .lede) {
  max-width: 760px;
  color: var(--muted);
}

.sequence-panel {
  align-self: start;
  border: 1px solid var(--line);
  background: var(--panel);
  box-shadow: var(--shadow);
  padding: 22px;
}

.sequence-panel h2 {
  margin-bottom: 18px;
  font-size: 1.35rem;
}

.sequence {
  display: grid;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: sequence;
}

.sequence li {
  counter-increment: sequence;
  display: grid;
  grid-template-columns: 34px 1fr;
  align-items: center;
  min-height: 38px;
  border: 1px solid var(--line);
  background: var(--subtle);
}

.sequence li::before {
  content: counter(sequence, decimal-leading-zero);
  display: grid;
  place-items: center;
  height: 100%;
  border-right: 1px solid var(--line);
  color: var(--accent);
  font-size: 0.72rem;
  font-weight: 700;
}

.sequence span {
  padding: 7px 10px;
  font-size: 0.94rem;
}

.control-band {
  display: grid;
  grid-template-columns: minmax(260px, 1fr) auto;
  gap: 12px 18px;
  align-items: end;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto 30px;
  padding: 18px;
  border-block: 1px solid var(--line);
  background: var(--subtle);
}

.search-label {
  grid-column: 1 / -1;
  color: var(--muted);
  font-size: 0.84rem;
  font-weight: 650;
}

input[type="search"] {
  width: 100%;
  min-height: 44px;
  border: 1px solid #b8c2be;
  background: var(--panel);
  color: var(--ink);
  padding: 0 14px;
  font: inherit;
}

input[type="search"]:focus,
button:focus-visible,
a:focus-visible {
  outline: 3px solid rgba(138, 90, 43, 0.28);
  outline-offset: 2px;
}

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

.filter-button {
  min-height: 44px;
  border: 1px solid #b8c2be;
  background: var(--panel);
  color: var(--ink);
  padding: 0 14px;
  font: inherit;
  cursor: pointer;
}

.filter-button.is-active {
  border-color: var(--accent);
  background: var(--accent);
  color: #ffffff;
}

[data-theme="dark"] .filter-button.is-active {
  color: #10201b;
}

.page-grid {
  display: grid;
  grid-template-columns: 220px minmax(0, 1fr);
  gap: 42px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
}

.toc {
  position: sticky;
  top: 92px;
  align-self: start;
  display: grid;
  gap: 8px;
  border-left: 2px solid var(--line);
  padding-left: 16px;
}

.toc p {
  margin: 0 0 6px;
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.toc a {
  color: var(--muted);
  font-size: 0.92rem;
  text-decoration: none;
}

.toc a.is-current {
  color: var(--accent);
  font-weight: 700;
}

.content {
  min-width: 0;
}

.section-block {
  padding: 36px 0;
  border-top: 1px solid var(--line);
}

.section-block:first-child {
  border-top: 0;
  padding-top: 0;
}

.compact-section {
  padding: 24px 0 36px;
}

.section-block > p,
.section-heading p {
  max-width: 840px;
  color: var(--muted);
}

.section-heading {
  display: flex;
  justify-content: space-between;
  gap: 24px;
  margin-bottom: 20px;
}

.result-count {
  flex: 0 0 auto;
  margin: 8px 0 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.model-list {
  display: grid;
  gap: 14px;
}

.model-entry {
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 22px;
  box-shadow: var(--shadow);
}

.model-entry.is-hidden {
  display: none;
}

.model-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 10px;
}

.model-meta span {
  border: 1px solid var(--line);
  background: var(--subtle);
  color: var(--muted);
  padding: 3px 8px;
  font-size: 0.76rem;
  font-weight: 650;
}

.model-entry p {
  margin: 10px 0 16px;
  color: color-mix(in srgb, var(--ink) 82%, var(--muted));
}

dl {
  display: grid;
  gap: 10px;
  margin: 0;
}

dl div {
  display: grid;
  grid-template-columns: 190px minmax(0, 1fr);
  gap: 14px;
  padding-top: 10px;
  border-top: 1px solid var(--line);
}

dt {
  color: var(--accent);
  font-weight: 700;
}

dd {
  margin: 0;
  color: var(--muted);
}

.matrix {
  display: grid;
  border: 1px solid var(--line);
  background: var(--panel);
}

.matrix > div {
  display: grid;
  grid-template-columns: 1fr 0.8fr 1.5fr;
  border-top: 1px solid var(--line);
}

.matrix > div:first-child {
  border-top: 0;
}

.matrix span {
  padding: 12px;
  border-left: 1px solid var(--line);
}

.matrix span:first-child {
  border-left: 0;
}

.matrix-head {
  background: var(--accent-soft);
  color: var(--ink);
  font-weight: 700;
}

.practice-list {
  display: grid;
  gap: 12px;
  margin: 18px 0 0;
  padding-left: 22px;
}

.practice-list li {
  padding-left: 4px;
  color: var(--muted);
}

.practice-list strong {
  color: var(--ink);
}

.bibliography-list {
  margin: 18px 0 0;
  padding-left: 22px;
  color: var(--muted);
}

.bibliography-list li + li {
  margin-top: 10px;
}

.text-link {
  color: var(--accent);
  font-weight: 700;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

.reference-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  margin-top: 18px;
}

.reference-link {
  display: grid;
  gap: 6px;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 18px;
  box-shadow: var(--shadow);
  text-decoration: none;
}

.reference-link span {
  color: var(--ink);
  font-weight: 700;
}

.reference-link small {
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.45;
}

.reference-link:hover span {
  color: var(--accent);
}

.course-catalog-hero {
  padding-bottom: 22px;
}

.portal-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto 34px;
}

.portal-card {
  display: grid;
  gap: 8px;
  min-height: 150px;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 18px;
  box-shadow: var(--shadow);
  text-decoration: none;
}

.portal-card:hover {
  border-color: var(--accent);
}

.portal-card strong {
  color: var(--ink);
  font-size: 1.15rem;
}

.portal-card small,
.course-meta {
  color: var(--muted);
  line-height: 1.45;
}

.portal-label {
  color: var(--accent);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.continue-card,
.boundary-card.is-primary {
  background: var(--accent-soft);
}

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

.boundary-card {
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 18px;
}

.boundary-card ul {
  margin: 12px 0 0;
  padding-left: 20px;
  color: var(--muted);
}

.course-path {
  display: grid;
  gap: 12px;
  width: min(980px, calc(100% - 32px));
  margin: 0 auto 42px;
}

.course-path-card {
  display: grid;
  grid-template-columns: 56px minmax(0, 1fr);
  gap: 4px 18px;
  align-items: center;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 18px;
  box-shadow: var(--shadow);
  text-decoration: none;
}

.course-path-card:hover {
  border-color: var(--accent);
}

.course-path-card.is-primary {
  background: var(--accent-soft);
}

.course-number {
  grid-row: span 2;
  color: var(--accent);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 1.45rem;
}

.course-title {
  color: var(--ink);
  font-weight: 750;
}

.course-path-card small {
  color: var(--muted);
  line-height: 1.45;
}

.course-support {
  display: grid;
  gap: 36px;
  width: min(980px, calc(100% - 32px));
  margin: 0 auto;
}

.course-dashboard {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto 42px;
}

.course-dashboard-card {
  display: grid;
  gap: 14px;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 20px;
  box-shadow: var(--shadow);
}

.course-dashboard-card.is-primary {
  background: var(--accent-soft);
}

.course-card-head {
  display: flex;
  gap: 16px;
  align-items: flex-start;
}

.course-card-head h2 {
  font-size: 1.45rem;
}

.course-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
}

.course-support-row {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
  width: min(1180px, calc(100% - 32px));
  margin: -16px auto 34px;
}

.course-support-row a {
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 12px 14px;
  color: var(--muted);
  text-decoration: none;
  box-shadow: var(--shadow);
}

.course-support-row a:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.course-flow {
  display: grid;
  grid-template-columns: 1fr minmax(220px, 1.2fr) 1fr;
  gap: 10px;
  width: min(1180px, calc(100% - 32px));
  margin: -10px auto 34px;
}

.course-flow a,
.course-flow-disabled {
  display: grid;
  gap: 4px;
  min-height: 70px;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 12px 14px;
  text-decoration: none;
  color: var(--ink);
  box-shadow: var(--shadow);
}

.course-flow a:hover {
  border-color: var(--accent);
}

.course-flow span {
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.course-flow-home {
  text-align: center;
}

.course-flow-disabled {
  color: var(--muted);
}

.source-frame {
  width: 100%;
  min-height: 360px;
  border: 1px solid var(--line);
  background: var(--panel);
}

.tall-source-frame {
  min-height: 520px;
}

[data-theme="dark"] .source-frame {
  filter: invert(1) hue-rotate(180deg);
}

.formula-list {
  display: grid;
  gap: 10px;
  margin-top: 18px;
}

.formula-list p {
  margin: 0;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 12px 14px;
  color: color-mix(in srgb, var(--ink) 82%, var(--muted));
  font-family: Consolas, "Courier New", monospace;
  font-size: 0.95rem;
}

.formula-strip,
.diagram-chain {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 18px;
}

.formula-strip span,
.diagram-chain span {
  position: relative;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 10px 14px;
  color: color-mix(in srgb, var(--ink) 82%, var(--muted));
  font-weight: 650;
}

.formula-strip span:not(:last-child)::after,
.diagram-chain span:not(:last-child)::after {
  content: "->";
  position: absolute;
  right: -21px;
  color: var(--accent);
  font-weight: 700;
}

.diagram-chain {
  gap: 26px;
}

.diagram-secondary span {
  background: var(--accent-soft);
}

.study-shell {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: 32px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
}

.study-sidebar {
  position: sticky;
  top: 92px;
  align-self: start;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 18px;
  box-shadow: var(--shadow);
}

.study-label {
  margin: 0 0 10px;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.progress-track {
  height: 10px;
  border: 1px solid var(--line);
  background: var(--subtle);
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--accent);
  transition: width 160ms ease;
}

.progress-text {
  margin: 10px 0 16px;
  color: var(--muted);
  font-size: 0.92rem;
}

.lesson-nav {
  display: grid;
  gap: 8px;
}

.lesson-tab {
  min-height: 42px;
  border: 1px solid var(--line);
  background: var(--panel);
  color: var(--ink);
  padding: 8px 10px;
  text-align: left;
  font: inherit;
  cursor: pointer;
}

.lesson-tab.is-active {
  border-color: var(--accent);
  background: var(--accent-soft);
  color: var(--ink);
  font-weight: 700;
}

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

.lesson {
  display: none;
  border-top: 1px solid var(--line);
  padding-top: 28px;
}

.lesson.is-active {
  display: block;
}

.lesson > p {
  max-width: 840px;
  color: var(--muted);
}

.study-card,
.quiz-block,
.diagnostic-exercise,
.definition-box,
.worked-example,
.misconception-box,
.guided-practice {
  margin-top: 18px;
  border: 1px solid var(--line);
  background: var(--panel);
  padding: 18px;
  box-shadow: var(--shadow);
}

.study-card h3 {
  margin-bottom: 8px;
}

.worked-example {
  border-left: 3px solid var(--accent);
}

.misconception-box {
  border-left: 3px solid var(--focus);
  background: color-mix(in srgb, var(--panel) 90%, var(--focus));
}

.guided-practice {
  background: var(--subtle);
}

.teaching-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  margin-top: 18px;
}

.reveal-panel {
  display: none;
  margin: 14px 0 0;
  color: var(--muted);
}

.reveal-panel.is-visible {
  display: block;
}

.reveal-answer {
  min-height: 40px;
  border: 1px solid var(--accent);
  background: var(--panel);
  color: var(--accent);
  padding: 0 12px;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
}

.quiz-block {
  display: grid;
  gap: 10px;
}

.quiz-block legend {
  color: var(--accent);
  font-weight: 700;
}

.quiz-block label {
  display: block;
  color: color-mix(in srgb, var(--ink) 82%, var(--muted));
}

.check-answer,
.complete-lesson,
#check-diagnostic {
  width: fit-content;
  min-height: 42px;
  border: 1px solid var(--accent);
  background: var(--accent);
  color: #ffffff;
  padding: 0 14px;
  font: inherit;
  cursor: pointer;
}

.complete-lesson {
  margin-top: 22px;
}

.complete-lesson:disabled {
  border-color: var(--line);
  background: var(--subtle);
  color: var(--muted);
  cursor: default;
}

.feedback {
  margin: 4px 0 0;
  font-weight: 650;
}

.feedback.is-correct {
  color: var(--accent);
}

.feedback.is-incorrect {
  color: #8a3d2b;
}

.feedback.is-neutral {
  color: var(--muted);
}

.term-match {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 18px;
}

.term-match button {
  min-height: 40px;
  border: 1px solid var(--line);
  background: var(--panel);
  color: var(--ink);
  padding: 0 12px;
  font: inherit;
  cursor: pointer;
}

.term-match button.is-active {
  border-color: var(--accent);
  background: var(--accent-soft);
  font-weight: 700;
}

.diagnostic-exercise {
  display: grid;
  gap: 10px;
}

.diagnostic-exercise select {
  max-width: 420px;
  min-height: 42px;
  border: 1px solid #b8c2be;
  background: var(--panel);
  color: var(--ink);
  padding: 0 10px;
  font: inherit;
}

@media (max-width: 900px) {
  .site-header {
    position: static;
  }

  .header-inner {
    align-items: center;
    text-align: center;
    flex-direction: column;
    padding: 14px 0;
  }

  nav {
    justify-content: center;
    flex-wrap: wrap;
    width: 100%;
    padding-bottom: 2px;
    gap: 12px 18px;
  }

  nav a {
    white-space: nowrap;
  }

  .intro-section,
  .page-grid,
  .control-band,
  .reference-grid,
  .portal-grid,
  .boundary-grid,
  .course-dashboard,
  .study-shell,
  .teaching-grid,
  .course-support-row,
  .course-flow {
    grid-template-columns: 1fr;
  }

  .study-sidebar {
    position: static;
  }

  .toc {
    position: static;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    border-left: 0;
    border-top: 1px solid var(--line);
    padding: 14px 0 0;
  }

  .toc p {
    grid-column: 1 / -1;
  }

  .section-heading {
    display: block;
  }
}

@media (max-width: 640px) {
  body {
    font-size: 15px;
  }

  .intro-section {
    padding-top: 34px;
  }

  h1 {
    font-size: 2.35rem;
  }

  h2 {
    font-size: 1.7rem;
  }

  .control-band,
  .model-entry,
  .sequence-panel {
    padding: 16px;
  }

  dl div,
  .matrix > div {
    grid-template-columns: 1fr;
  }

  .matrix span {
    border-left: 0;
    border-top: 1px solid var(--line);
  }

  .matrix span:first-child {
    border-top: 0;
  }

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