:root {
  color-scheme: light;
  --paper: #ffffff;
  --surface: #ffffff;
  --surface-blue: #f5faff;
  --surface-strong: #e8f4fd;
  --ink: #25272a;
  --ink-strong: #101317;
  --muted: #5f6368;
  --faint: #8a9097;
  --line: #e5e7eb;
  --line-strong: #cbd2d9;
  --blue: #2196f3;
  --blue-hover: #1976d2;
  --blue-active: #0d47a1;
  --green: #2e7d32;
  --green-bg: #f1faf2;
  --red: #c62828;
  --red-bg: #fff5f5;
  --amber: #8a5a00;
  --amber-bg: #fffaf0;
  --radius-sm: 0.5rem;
  --radius-md: 0.8rem;
  --radius-lg: 1.2rem;
  --shadow-float: 0 1rem 2.5rem rgb(16 19 23 / 0.08);
  --page-gutter: clamp(1rem, 4vw, 2.5rem);
  --content-wide: 88rem;
  --content-prose: 52rem;
  --ease-out: cubic-bezier(0.22, 1, 0.36, 1);
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

[hidden] {
  display: none !important;
}

.sr-only {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  margin: -1px !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  clip-path: inset(50%) !important;
  white-space: nowrap !important;
}

html {
  scroll-behavior: smooth;
  text-size-adjust: 100%;
  overflow-x: clip;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-size: 1rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  overflow-x: clip;
}

button,
input,
select,
textarea,
math-field {
  font: inherit;
}

button,
summary,
a,
input,
select,
textarea,
math-field {
  -webkit-tap-highlight-color: transparent;
}

a {
  color: var(--blue-hover);
  text-underline-offset: 0.2em;
}

a:hover {
  color: var(--blue-active);
}

img,
svg {
  display: block;
  max-width: 100%;
}

h1,
h2,
h3 {
  color: var(--ink-strong);
  font-weight: 720;
  letter-spacing: -0.025em;
  line-height: 1.14;
  text-wrap: balance;
}

h1 {
  margin: 0;
  font-size: clamp(2.25rem, 6vw, 4.5rem);
}

h2 {
  margin: 0 0 1.25rem;
  font-size: clamp(1.75rem, 3.5vw, 2.6rem);
}

h3 {
  margin: 0 0 0.6rem;
  font-size: 1.25rem;
}

p,
ul,
ol {
  margin-block: 0 1rem;
}

.skip-link {
  position: fixed;
  z-index: 100;
  top: 0.75rem;
  left: 0.75rem;
  transform: translateY(-180%);
  border-radius: var(--radius-sm);
  background: var(--ink-strong);
  color: var(--surface);
  padding: 0.65rem 0.9rem;
  transition: transform 160ms var(--ease-out);
}

.skip-link:focus {
  transform: translateY(0);
}

:focus-visible {
  outline: 3px solid var(--blue);
  outline-offset: 3px;
}

.site-header {
  position: relative;
  z-index: 20;
  border-bottom: 1px solid var(--line);
  background: rgb(255 255 255 / 0.96);
}

.header-inner,
.footer-inner,
.footer-meta {
  width: min(100%, var(--content-wide));
  margin-inline: auto;
  padding-inline: var(--page-gutter);
}

.header-inner {
  min-height: 4.5rem;
  display: flex;
  align-items: center;
  gap: 1.5rem;
}

.wordmark {
  display: inline-flex;
  align-items: center;
  gap: 0.65rem;
  color: var(--ink-strong);
  font-size: 1rem;
  font-weight: 750;
  letter-spacing: -0.02em;
  text-decoration: none;
}

.wordmark-mark {
  display: grid;
  width: 2rem;
  height: 2rem;
  place-items: center;
  border-radius: 0.62rem;
  background: var(--blue);
  color: var(--surface);
  font-family: Georgia, serif;
  font-size: 1.4rem;
  font-weight: 700;
}

.nav-shell {
  display: none;
  margin-left: auto;
}

.desktop-nav {
  margin-left: auto;
}

.nav-shell summary {
  display: none;
}

.primary-nav {
  display: flex;
  align-items: center;
  gap: 0.2rem;
}

.primary-nav a {
  min-height: 2.75rem;
  display: inline-flex;
  align-items: center;
  border-radius: var(--radius-sm);
  color: var(--muted);
  padding: 0.55rem 0.8rem;
  font-size: 0.92rem;
  font-weight: 640;
  text-decoration: none;
}

.primary-nav a:hover {
  background: var(--surface-blue);
  color: var(--ink-strong);
}

.primary-nav a[aria-current="page"] {
  background: var(--surface-strong);
  color: var(--blue-active);
}

.mathos-link {
  min-height: 2.75rem;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  color: var(--ink);
  padding: 0.5rem 0.75rem;
  font-size: 0.82rem;
  font-weight: 650;
  text-decoration: none;
}

.mathos-link:hover {
  border-color: var(--blue);
  background: var(--surface-blue);
}

.page-shell {
  width: min(100%, var(--content-wide));
  margin-inline: auto;
  padding-inline: var(--page-gutter);
}

.breadcrumbs {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin: 0;
  padding: 1.25rem 0 0;
  color: var(--muted);
  font-size: 0.84rem;
  list-style: none;
}

.breadcrumbs a {
  color: inherit;
}

.breadcrumbs li + li::before {
  content: "/";
  margin-right: 0.5rem;
  color: var(--faint);
}

.eyebrow {
  margin: 0 0 0.7rem;
  color: var(--blue-active);
  font-size: 0.78rem;
  font-weight: 760;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.lede {
  max-width: 66ch;
  margin: 1.15rem 0 0;
  color: var(--muted);
  font-size: clamp(1.05rem, 2vw, 1.24rem);
  line-height: 1.55;
}

.page-intro {
  padding-block: clamp(2rem, 5vw, 3.5rem) clamp(1.5rem, 3vw, 2.25rem);
}

.page-intro.compact {
  max-width: 58rem;
  padding-bottom: 2rem;
}

.byline {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem 0.65rem;
  align-items: center;
  margin-top: 1.25rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.byline a {
  font-weight: 650;
}

.dot-separator::before {
  content: "·";
  margin-right: 0.65rem;
  color: var(--faint);
}

.section {
  padding-block: clamp(3.5rem, 8vw, 6rem);
}

.section-tight {
  padding-block: clamp(2.5rem, 5vw, 4rem);
}

.section-heading {
  max-width: 46rem;
  margin-bottom: 2rem;
}

.section-heading p {
  max-width: 64ch;
  color: var(--muted);
  font-size: 1.05rem;
}

.surface-band {
  border-block: 1px solid var(--line);
  background: var(--surface);
}

.button {
  min-height: 3rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  border: 1px solid transparent;
  border-radius: var(--radius-sm);
  padding: 0.68rem 1rem;
  font-weight: 720;
  line-height: 1.2;
  text-decoration: none;
  cursor: pointer;
  transition: background-color 160ms var(--ease-out), border-color 160ms var(--ease-out), color 160ms var(--ease-out), transform 160ms var(--ease-out);
}

.button:hover {
  transform: translateY(-1px);
}

.button:active {
  transform: translateY(0);
}

.button-primary {
  background: var(--blue-hover);
  color: var(--surface);
}

.button-primary:hover {
  background: var(--blue-active);
  color: var(--surface);
}

.button-secondary {
  border-color: var(--line-strong);
  background: var(--surface);
  color: var(--ink);
}

.button-secondary:hover {
  border-color: var(--blue);
  background: var(--surface-blue);
  color: var(--ink-strong);
}

.button-quiet {
  min-height: 2.5rem;
  border-color: var(--line);
  background: transparent;
  color: var(--muted);
  padding: 0.45rem 0.7rem;
  font-size: 0.84rem;
}

.text-link {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  font-weight: 700;
}

.katex-display {
  margin: 1.25rem 0;
  overflow-x: auto;
  overflow-y: hidden;
  padding-block: 0.25rem;
}

.formula-stage {
  border-left: 3px solid var(--blue);
  background: var(--surface);
  padding: clamp(1rem, 3vw, 1.75rem);
}

.formula-stage .katex-display {
  font-size: clamp(1.1rem, 2.5vw, 1.45rem);
}

.inline-note {
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  background: var(--surface-blue);
  padding: 1rem 1.1rem;
}

.inline-note strong {
  color: var(--ink-strong);
}

.solver-hero {
  display: grid;
  grid-template-columns: minmax(17rem, 0.72fr) minmax(32rem, 1.28fr);
  gap: clamp(2rem, 5vw, 5rem);
  align-items: start;
  padding-block: clamp(2.5rem, 7vw, 5rem) clamp(4rem, 8vw, 6.5rem);
}

.solver-hero > *,
.expression-field,
.context-fields,
.operation-options {
  min-width: 0;
}

.solver-intro {
  position: sticky;
  top: 2rem;
  padding-top: 1.4rem;
}

.solver-intro h1 {
  max-width: 8ch;
}

.trust-line {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem 1rem;
  margin-top: 1.5rem;
  color: var(--muted);
  font-size: 0.84rem;
  font-weight: 620;
}

.trust-line span span {
  color: var(--green);
  font-weight: 800;
}

.calculator-shell {
  min-width: 0;
  position: relative;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  background-color: var(--surface);
  background-image: none;
  box-shadow: var(--shadow-float);
  overflow: clip;
}

#solver-form {
  min-width: 0;
  background: var(--surface);
  padding: clamp(1rem, 3vw, 1.6rem);
}

.operation-picker {
  min-width: 0;
  margin: 0 0 1.35rem;
  border: 0;
  padding: 0;
}

.operation-picker legend,
.field-label-row label,
.compact-field > span {
  color: var(--ink-strong);
  font-size: 0.85rem;
  font-weight: 720;
}

.operation-picker legend {
  margin-bottom: 0.6rem;
}

.operation-options {
  display: flex;
  gap: 0.4rem;
  overflow-x: auto;
  padding: 0.2rem;
  scrollbar-width: thin;
}

.operation-options label {
  flex: 0 0 auto;
  cursor: pointer;
}

.operation-options input {
  position: absolute;
  opacity: 0;
  pointer-events: none;
}

.operation-options span {
  min-height: 2.75rem;
  display: inline-flex;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--muted);
  padding: 0.55rem 0.8rem;
  font-size: 0.86rem;
  font-weight: 670;
  white-space: nowrap;
  transition: background-color 160ms var(--ease-out), border-color 160ms var(--ease-out), color 160ms var(--ease-out);
}

.operation-options input:checked + span {
  border-color: var(--blue);
  background: var(--surface-blue);
  color: var(--blue-active);
}

.operation-options input:focus-visible + span {
  outline: 3px solid var(--blue);
  outline-offset: 2px;
}

.field-label-row {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: end;
  margin-bottom: 0.5rem;
}

.field-label-row span {
  color: var(--muted);
  font-size: 0.76rem;
  text-align: right;
}

.expression-field textarea,
.expression-field math-field,
.compact-field input,
.compact-field select {
  width: 100%;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--ink);
  transition: border-color 160ms var(--ease-out), box-shadow 160ms var(--ease-out);
}

.expression-field textarea {
  min-height: 7.5rem;
  resize: vertical;
  padding: 1rem;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  font-size: clamp(1rem, 2vw, 1.18rem);
  line-height: 1.55;
}

.expression-field math-field {
  min-height: 7.5rem;
  display: block;
  padding: 1rem;
  font-size: clamp(1.28rem, 3vw, 1.7rem);
  line-height: 1.45;
  --caret-color: var(--blue-active);
  --selection-background-color: rgb(33 150 243 / 0.18);
  --contains-highlight-background-color: rgb(33 150 243 / 0.1);
  --placeholder-color: var(--faint);
  --smart-fence-color: var(--blue-active);
}

.math-input-toolbar {
  display: flex;
  gap: 0.35rem;
  margin-top: 0.45rem;
  overflow-x: auto;
  padding: 0.15rem 0.1rem;
  scrollbar-width: thin;
}

.math-input-toolbar button {
  min-width: 2.7rem;
  min-height: 2.5rem;
  flex: 0 0 auto;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--ink-strong);
  padding: 0.3rem 0.6rem;
  cursor: pointer;
}

.math-input-toolbar button:hover {
  border-color: var(--blue);
  background: var(--surface-blue);
}

.math-input-toolbar button:focus-visible {
  outline: 3px solid rgb(33 150 243 / 0.24);
  outline-offset: 1px;
}

.math-keyboard-dismiss {
  position: fixed;
  z-index: 10000;
  top: 0.75rem;
  right: max(0.75rem, calc((100vw - 62rem) / 2));
  min-height: 2.75rem;
  border: 1px solid var(--line-strong);
  border-radius: 100vmax;
  background: var(--surface);
  box-shadow: 0 0.45rem 1.5rem rgb(16 19 23 / 0.16);
  color: var(--ink-strong);
  padding: 0.55rem 0.85rem;
  font-size: 0.82rem;
  font-weight: 700;
  cursor: pointer;
}

.math-keyboard-dismiss:hover {
  border-color: var(--blue);
  background: var(--surface-blue);
}

.expression-field textarea:focus,
.expression-field math-field:focus-within,
.compact-field input:focus,
.compact-field select:focus {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px rgb(33 150 243 / 0.16);
  outline: 0;
}

.field-error {
  margin: 0.45rem 0 0;
  color: var(--red);
  font-size: 0.84rem;
  font-weight: 650;
}

.context-fields {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
  margin-top: 0.9rem;
}

.compact-field {
  display: grid;
  gap: 0.35rem;
}

.compact-field small {
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 500;
}

.compact-field input,
.compact-field select {
  min-height: 2.8rem;
  padding: 0.55rem 0.7rem;
}

.solver-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.65rem;
  margin-top: 1.2rem;
}

.solve-button {
  min-width: 8.5rem;
}

.solve-button[aria-busy="true"] {
  cursor: wait;
  opacity: 0.78;
}

.calculation-status {
  color: var(--muted);
  font-size: 0.82rem;
}

.example-strip {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  margin: 1.25rem -0.15rem -0.15rem;
  overflow-x: auto;
  padding: 0.15rem;
  scrollbar-width: thin;
}

.example-strip > span {
  flex: 0 0 auto;
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 650;
}

.example-strip button {
  min-height: 2.4rem;
  flex: 0 0 auto;
  border: 1px solid var(--line);
  border-radius: 100vmax;
  background: var(--surface);
  color: var(--muted);
  padding: 0.4rem 0.7rem;
  font-size: 0.75rem;
  cursor: pointer;
}

.example-strip button:hover {
  border-color: var(--blue);
  color: var(--blue-active);
}

.result-panel {
  border-top: 1px solid var(--line-strong);
  background: var(--surface);
  padding: clamp(1.2rem, 3vw, 1.75rem);
}

.result-heading {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: start;
}

.result-kicker {
  margin: 0 0 0.15rem;
  color: var(--green);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.result-heading h2 {
  margin: 0;
  font-size: 1.45rem;
}

.interpreted-problem {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 1rem;
  align-items: center;
  margin-top: 1rem;
  border-block: 1px solid var(--line);
  padding-block: 0.7rem;
}

.interpreted-problem > span,
.result-conditions strong {
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 760;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

#interpreted-problem-formula {
  min-width: 0;
  overflow-x: auto;
  text-align: right;
}

.result-formula {
  min-height: 6.5rem;
  display: grid;
  align-items: center;
  margin-top: 1rem;
  border-radius: var(--radius-md);
  background: var(--surface-blue);
  padding: 1rem;
  overflow-x: auto;
}

.result-formula .katex-display {
  margin: 0;
  font-size: clamp(1.1rem, 3vw, 1.5rem);
}

.plain-answer {
  margin: 0.55rem 0 0;
  color: var(--muted);
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  font-size: 0.76rem;
  overflow-wrap: anywhere;
}

.result-conditions {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 0.7rem;
  align-items: baseline;
  margin-top: 0.9rem;
  border-radius: var(--radius-sm);
  background: #fafafa;
  padding: 0.7rem 0.8rem;
}

.result-conditions p {
  margin: 0;
  color: var(--muted);
  font-size: 0.82rem;
}

.solution-steps {
  margin-top: 1.5rem;
}

.solution-steps h3 {
  font-size: 1rem;
}

.solution-steps ol {
  display: grid;
  gap: 0.75rem;
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: solution-step;
}

.solution-steps li {
  display: grid;
  grid-template-columns: 1.8rem minmax(0, 1fr);
  gap: 0.7rem;
  counter-increment: solution-step;
}

.solution-steps li::before {
  content: counter(solution-step);
  width: 1.65rem;
  height: 1.65rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-strong);
  color: var(--blue-active);
  font-size: 0.74rem;
  font-weight: 800;
}

.step-title {
  display: block;
  color: var(--ink-strong);
  font-size: 0.9rem;
  font-weight: 720;
}

.step-copy {
  margin: 0.18rem 0 0;
  color: var(--muted);
  font-size: 0.88rem;
}

.step-formula {
  margin-top: 0.35rem;
  overflow-x: auto;
}

.verification {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 0.75rem;
  margin-top: 1.5rem;
  border: 1px solid #9dcca0;
  border-radius: var(--radius-md);
  background: var(--green-bg);
  padding: 0.9rem 1rem;
}

.verification[data-status="caution"] {
  border-color: #d9bd80;
  background: var(--amber-bg);
}

.verification[data-status="error"] {
  border-color: #e2a3a3;
  background: var(--red-bg);
}

.verification-icon {
  width: 1.55rem;
  height: 1.55rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--green);
  color: var(--surface);
  font-size: 0.78rem;
  font-weight: 900;
}

.verification[data-status="caution"] .verification-icon {
  background: var(--amber);
}

.verification[data-status="error"] .verification-icon {
  background: var(--red);
}

.verification strong {
  display: block;
  color: var(--ink-strong);
  font-size: 0.88rem;
}

.verification p {
  margin: 0.15rem 0 0;
  color: var(--muted);
  font-size: 0.82rem;
}

.capability-list {
  border-top: 1px solid var(--line);
}

.capability-list article {
  display: grid;
  grid-template-columns: 3rem minmax(14rem, 1fr) minmax(12rem, 0.65fr);
  gap: 1.5rem;
  align-items: center;
  border-bottom: 1px solid var(--line);
  padding-block: 1.4rem;
}

.capability-number {
  color: var(--blue-active);
  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: 0.78rem;
  font-weight: 700;
}

.capability-list h3,
.capability-list p {
  margin: 0;
}

.capability-list p {
  max-width: 62ch;
  margin-top: 0.35rem;
  color: var(--muted);
  font-size: 0.94rem;
}

.capability-list code {
  justify-self: start;
  border-radius: var(--radius-sm);
  background: var(--surface-blue);
  color: var(--ink-strong);
  padding: 0.55rem 0.7rem;
  font-size: 0.78rem;
  overflow-wrap: anywhere;
}

.method-pair {
  display: grid;
  gap: 1rem;
}

.method-feature {
  min-height: 19rem;
  display: grid;
  grid-template-columns: minmax(16rem, 0.75fr) minmax(20rem, 1.25fr);
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  overflow: clip;
}

.method-feature-copy {
  align-self: center;
  padding: clamp(1.5rem, 4vw, 3rem);
}

.method-label {
  margin: 0 0 0.35rem;
  color: var(--blue-active);
  font-size: 0.76rem;
  font-weight: 760;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.method-feature-copy h3 {
  font-size: clamp(1.7rem, 3vw, 2.25rem);
}

.method-feature-copy p:not(.method-label) {
  color: var(--muted);
}

.method-mini-formula {
  min-width: 0;
  display: grid;
  align-content: center;
  background: var(--surface-blue);
  padding: clamp(1.5rem, 5vw, 4rem);
  text-align: center;
}

.method-feature-parts .method-mini-formula {
  background: var(--amber-bg);
}

.method-mini-formula span {
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 680;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.accuracy-layout {
  display: grid;
  grid-template-columns: minmax(17rem, 0.75fr) minmax(23rem, 1.25fr);
  gap: clamp(2rem, 7vw, 6rem);
  align-items: start;
}

.lede-small {
  max-width: 60ch;
  color: var(--muted);
  font-size: 1.05rem;
}

.check-sequence {
  display: grid;
  gap: 0;
  margin: 0;
  padding: 0;
  list-style: none;
}

.check-sequence li {
  display: grid;
  grid-template-columns: 2.6rem minmax(0, 1fr);
  gap: 1rem;
  border-bottom: 1px solid var(--line);
  padding: 1.1rem 0;
}

.check-sequence li:first-child {
  padding-top: 0;
}

.check-sequence li > span {
  width: 2.25rem;
  height: 2.25rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-strong);
  color: var(--blue-active);
  font-weight: 800;
}

.check-sequence strong {
  display: block;
  color: var(--ink-strong);
}

.check-sequence p {
  margin: 0.2rem 0 0;
  color: var(--muted);
  font-size: 0.92rem;
}

.how-to-list {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  margin: 0;
  border-block: 1px solid var(--line);
  padding: 0;
  list-style: none;
}

.how-to-list li {
  display: grid;
  grid-template-columns: 2.2rem minmax(0, 1fr);
  gap: 0.8rem;
  padding: 1.35rem clamp(1rem, 2.5vw, 1.8rem);
}

.how-to-list li + li {
  border-left: 1px solid var(--line);
}

.how-to-list li > span {
  width: 2rem;
  height: 2rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-strong);
  color: var(--blue-active);
  font-size: 0.78rem;
  font-weight: 800;
}

.how-to-list h3,
.how-to-list p {
  margin: 0;
}

.how-to-list h3 {
  font-size: 1rem;
}

.how-to-list p {
  margin-top: 0.25rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.input-guide {
  display: grid;
  grid-template-columns: minmax(20rem, 1.15fr) minmax(17rem, 0.85fr);
  gap: clamp(2rem, 6vw, 5rem);
  align-items: start;
  margin-top: clamp(2.5rem, 5vw, 4rem);
}

.syntax-table-wrap {
  overflow-x: auto;
}

.syntax-table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
}

.syntax-table caption {
  margin-bottom: 0.65rem;
  color: var(--muted);
  font-size: 0.82rem;
  text-align: left;
}

.syntax-table th,
.syntax-table td {
  border-bottom: 1px solid var(--line);
  padding: 0.8rem;
}

.syntax-table th {
  color: var(--muted);
  font-size: 0.76rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.syntax-table td:first-child {
  color: var(--ink-strong);
  white-space: nowrap;
}

.complete-input-example {
  border-radius: var(--radius-md);
  background: var(--surface-blue);
  padding: clamp(1.25rem, 3vw, 2rem);
}

.complete-input-example h3 {
  margin: 0;
  font-size: 1.25rem;
}

.complete-input-example p {
  color: var(--muted);
  font-size: 0.92rem;
}

.complete-input-example .text-link,
.worked-check .text-link {
  color: var(--blue-active);
}

.example-groups {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: clamp(2rem, 5vw, 4rem) clamp(2rem, 7vw, 6rem);
}

.example-group h3 {
  margin: 0 0 0.45rem;
  color: var(--blue-active);
  font-size: 0.9rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.example-group ul {
  margin: 0;
  border-top: 1px solid var(--line-strong);
  padding: 0;
  list-style: none;
}

.example-group li {
  min-height: 4.6rem;
  display: flex;
  gap: 1rem;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--line);
  padding-block: 0.85rem;
}

.example-group li > div {
  min-width: 0;
  display: grid;
  gap: 0.25rem;
}

.example-group li span {
  color: var(--muted);
  font-size: 0.78rem;
}

.example-group button {
  min-width: 3.4rem;
  min-height: 2.75rem;
  flex: 0 0 auto;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--blue-active);
  font-size: 0.82rem;
  font-weight: 720;
  cursor: pointer;
}

.example-group button:hover {
  border-color: var(--blue);
  background: var(--surface-blue);
}

.solver-worked-example {
  display: grid;
  grid-template-columns: minmax(15rem, 0.62fr) minmax(27rem, 1.38fr);
  gap: clamp(2rem, 7vw, 6rem);
  align-items: start;
}

.worked-example-intro {
  position: sticky;
  top: 2rem;
}

.worked-example-intro p {
  max-width: 36ch;
  color: var(--muted);
}

.worked-example-intro .button {
  margin-top: 0.75rem;
}

.worked-solution {
  min-width: 0;
  border-top: 1px solid var(--line-strong);
}

.worked-problem {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 1rem;
  align-items: center;
  background: var(--surface-blue);
  padding: 1rem 1.2rem;
}

.worked-problem > span:first-child {
  color: var(--blue-active);
  font-size: 0.75rem;
  font-weight: 760;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.worked-problem .katex-display {
  margin: 0;
}

.worked-solution > ol {
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: worked-step;
}

.worked-solution > ol > li {
  display: grid;
  grid-template-columns: 2.25rem minmax(0, 1fr);
  gap: 1rem;
  border-bottom: 1px solid var(--line);
  padding-block: 1.25rem;
  counter-increment: worked-step;
}

.worked-solution > ol > li::before {
  content: counter(worked-step);
  width: 2rem;
  height: 2rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-strong);
  color: var(--blue-active);
  font-size: 0.78rem;
  font-weight: 800;
}

.worked-solution h3,
.worked-solution p {
  margin: 0;
}

.worked-solution h3 {
  font-size: 1.03rem;
}

.worked-solution p {
  max-width: 66ch;
  margin-top: 0.3rem;
  color: var(--muted);
  font-size: 0.92rem;
}

.worked-solution math-tex:not([display]) {
  display: inline-block;
  margin-top: 0.5rem;
}

.worked-check {
  margin-top: 1.25rem;
  border-radius: var(--radius-md);
  background: var(--green-bg);
  padding: 1rem 1.15rem;
}

.worked-check strong {
  color: var(--green);
}

.worked-check .katex-display {
  margin-block: 0.75rem;
}

.common-mistakes .mistake-list article {
  display: grid;
  grid-template-columns: minmax(14rem, 0.8fr) minmax(20rem, 1.2fr);
  gap: clamp(1.5rem, 5vw, 4rem);
  align-items: baseline;
  padding-block: 1.2rem;
}

.common-mistakes .mistake-list p {
  margin: 0;
}

.mathos-referral {
  position: relative;
  overflow: hidden;
  border-block: 1px solid #3b9ceb;
  background:
    radial-gradient(circle at 88% 12%, rgb(255 255 255 / 0.2), transparent 24rem),
    linear-gradient(120deg, var(--blue-active) 0%, var(--blue-hover) 58%, var(--blue) 100%);
  color: var(--surface);
}

.mathos-referral::after {
  content: "∫";
  position: absolute;
  right: clamp(1rem, 7vw, 8rem);
  bottom: -7.5rem;
  color: rgb(255 255 255 / 0.08);
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(14rem, 24vw, 23rem);
  line-height: 1;
  pointer-events: none;
  transform: rotate(8deg);
}

.mathos-referral h2,
.mathos-referral .eyebrow {
  color: var(--surface);
}

.mathos-referral h2 {
  max-width: 24ch;
  margin-bottom: 1.25rem;
  font-size: clamp(2.25rem, 5vw, 4rem);
}

.mathos-referral h2 span {
  display: block;
}

.mathos-referral .eyebrow {
  color: #d7edff;
}

.mathos-referral p {
  max-width: 53ch;
  color: #f2f8fd;
}

.referral-inner {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  justify-content: space-between;
  gap: clamp(2rem, 7vw, 7rem);
  align-items: center;
}

.referral-button {
  flex: 0 0 auto;
  min-height: 3.65rem;
  background: var(--surface);
  box-shadow: 0 1rem 2.5rem rgb(8 45 93 / 0.22);
  color: var(--blue-active);
  padding-inline: 1.35rem;
}

.referral-button:hover {
  background: #eaf6ff;
  color: var(--blue-active);
}

.faq-list {
  width: 100%;
  border-top: 1px solid var(--line);
}

.faq-list details {
  border-bottom: 1px solid var(--line);
}

.faq-list summary {
  min-height: 3.6rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  color: var(--ink-strong);
  font-weight: 700;
  cursor: pointer;
  list-style: none;
}

.faq-list summary::-webkit-details-marker {
  display: none;
}

.faq-list summary::after {
  content: "+";
  color: var(--blue);
  font-size: 1.35rem;
  font-weight: 500;
}

.faq-list details[open] summary::after {
  content: "−";
}

.faq-list details p {
  width: 100%;
  padding: 0 clamp(2.5rem, 6vw, 6rem) 1.1rem 0;
  color: var(--muted);
}

.source-note {
  border-top: 1px solid var(--line);
  padding-block: 1.5rem 3.5rem;
}

.source-note h2 {
  margin: 0;
  font-size: 1rem;
}

.source-note p {
  max-width: 72ch;
  margin: 0.35rem 0 0;
  color: var(--muted);
  font-size: 0.85rem;
}

@media (max-width: 960px) {
  .solver-hero {
    grid-template-columns: minmax(0, 1fr);
    gap: 2rem;
  }

  .solver-intro {
    min-width: 0;
    position: static;
    padding-top: 0;
  }

  .solver-intro h1 {
    max-width: none;
  }

  .capability-list article {
    grid-template-columns: 2.5rem minmax(0, 1fr);
  }

  .capability-list code {
    grid-column: 2;
  }

  .how-to-list {
    grid-template-columns: 1fr;
  }

  .how-to-list li + li {
    border-top: 1px solid var(--line);
    border-left: 0;
  }
}

@media (max-width: 760px) {
  .method-feature,
  .accuracy-layout,
  .input-guide,
  .solver-worked-example {
    grid-template-columns: 1fr;
  }

  .worked-example-intro {
    position: static;
  }

  .example-groups {
    grid-template-columns: 1fr;
  }

  .common-mistakes .mistake-list article {
    grid-template-columns: 1fr;
    gap: 0.35rem;
  }

  .method-mini-formula {
    min-height: 13rem;
  }

  .referral-inner {
    align-items: flex-start;
    grid-template-columns: 1fr;
    gap: 2rem;
  }
}

@media (max-width: 540px) {
  .solver-hero {
    padding-top: 2rem;
  }

  .calculator-shell {
    margin-inline: -0.25rem;
    border-radius: var(--radius-md);
  }

  .field-label-row {
    align-items: start;
    flex-direction: column;
    gap: 0.2rem;
  }

  .field-label-row span {
    text-align: left;
  }

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

  .solver-actions .button {
    flex: 1;
  }

  .calculation-status {
    width: 100%;
  }

  .result-heading {
    align-items: center;
  }

  .interpreted-problem,
  .result-conditions,
  .worked-problem {
    grid-template-columns: 1fr;
    gap: 0.35rem;
  }

  #interpreted-problem-formula {
    text-align: left;
  }

  .capability-list article {
    grid-template-columns: 2rem minmax(0, 1fr);
    gap: 0.75rem;
  }

  .method-feature {
    min-height: 0;
  }

  .method-mini-formula {
    min-height: 11rem;
    padding-inline: 0.8rem;
  }
}

.source-list {
  padding-left: 1.2rem;
}

.source-list li + li {
  margin-top: 0.65rem;
}

.site-footer {
  border-top: 1px solid var(--line);
  background: var(--surface);
  padding-top: 3rem;
}

.footer-inner {
  display: grid;
  grid-template-columns: minmax(0, 1.4fr) minmax(16rem, 1fr);
  gap: 3rem;
}

.footer-inner p {
  max-width: 34rem;
  margin-top: 0.8rem;
  color: var(--muted);
}

.footer-inner nav {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.6rem 1rem;
  align-content: start;
}

.footer-inner nav a {
  color: var(--muted);
  font-size: 0.9rem;
}

.footer-meta {
  display: flex;
  justify-content: space-between;
  border-top: 1px solid var(--line);
  margin-top: 2.5rem;
  padding-block: 1rem 1.5rem;
  color: var(--muted);
  font-size: 0.8rem;
}

@media (max-width: 820px) {
  .header-inner {
    gap: 0.75rem;
  }

  .mathos-link {
    display: none;
  }

  .nav-shell {
    position: relative;
    display: block;
  }

  .nav-shell summary {
    min-height: 2.75rem;
    display: inline-flex;
    align-items: center;
    gap: 0.55rem;
    border: 1px solid var(--line);
    border-radius: var(--radius-sm);
    padding: 0.5rem 0.75rem;
    color: var(--ink);
    font-size: 0.9rem;
    font-weight: 680;
    cursor: pointer;
    list-style: none;
  }

  .nav-shell summary::-webkit-details-marker {
    display: none;
  }

  .nav-shell summary span,
  .nav-shell summary span::before,
  .nav-shell summary span::after {
    width: 1rem;
    height: 2px;
    display: block;
    border-radius: 1rem;
    background: currentColor;
  }

  .nav-shell summary span {
    position: relative;
  }

  .nav-shell summary span::before,
  .nav-shell summary span::after {
    position: absolute;
    content: "";
  }

  .nav-shell summary span::before {
    top: -0.32rem;
  }

  .nav-shell summary span::after {
    top: 0.32rem;
  }

  .primary-nav {
    position: absolute;
    top: calc(100% + 0.55rem);
    right: 0;
    width: min(19rem, calc(100vw - 2rem));
    display: grid;
    border: 1px solid var(--line);
    border-radius: var(--radius-md);
    background: var(--surface);
    box-shadow: var(--shadow-float);
    padding: 0.45rem;
  }

  .primary-nav.desktop-nav {
    display: none;
  }

  .nav-shell:not([open]) .primary-nav {
    display: none;
  }

  .footer-inner {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }
}

@media (max-width: 540px) {
  :root {
    --page-gutter: 1rem;
  }

  body {
    line-height: 1.6;
  }

  h1 {
    font-size: clamp(2.15rem, 12vw, 3rem);
  }

  .header-inner {
    min-height: 4rem;
  }

  .wordmark {
    font-size: 0.94rem;
  }

  .wordmark-mark {
    width: 1.8rem;
    height: 1.8rem;
    font-size: 1.2rem;
  }

  .breadcrumbs {
    overflow-x: auto;
    white-space: nowrap;
  }

  .byline {
    display: grid;
    gap: 0.25rem;
  }

  .dot-separator::before {
    display: none;
  }

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

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}

/* Tutorial documents */

.article-layout {
  display: grid;
  grid-template-columns: 12rem minmax(0, var(--content-prose));
  gap: clamp(2rem, 6vw, 5rem);
  justify-content: center;
  align-items: start;
  padding-bottom: clamp(4rem, 9vw, 7rem);
}

.article-outline {
  position: sticky;
  top: 1.5rem;
  border-left: 2px solid var(--line);
  padding-left: 1rem;
}

.article-outline > strong {
  color: var(--ink-strong);
  font-size: 0.8rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.article-outline nav {
  display: grid;
  gap: 0.55rem;
  margin-top: 0.8rem;
}

.article-outline a {
  color: var(--muted);
  font-size: 0.84rem;
  line-height: 1.4;
  text-decoration: none;
}

.article-outline a:hover {
  color: var(--blue-active);
}

.article-body {
  min-width: 0;
}

.lesson-section {
  padding-block: clamp(2.75rem, 6vw, 4.25rem);
  scroll-margin-top: 1.5rem;
}

.lesson-section + .lesson-section {
  border-top: 1px solid var(--line);
}

.lesson-first {
  padding-top: 0;
}

.question-label {
  margin: 0 0 0.55rem;
  color: var(--blue-active);
  font-size: 0.74rem;
  font-weight: 780;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.article-body h2 {
  font-size: clamp(1.75rem, 4vw, 2.45rem);
}

.article-body h3 {
  margin-top: 1.8rem;
}

.article-body p,
.article-body li {
  max-width: 72ch;
}

.formula-annotated {
  margin-block: 1.5rem;
}

.parts-formula {
  background: var(--surface);
}

.preflight-note {
  margin-top: 2.5rem;
  border-top: 1px solid var(--line);
  padding-top: 1.25rem;
  color: var(--muted);
  font-size: 0.92rem;
}

.preflight-note strong {
  color: var(--ink-strong);
}

.interactive-lab {
  margin-top: 2rem;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  background: var(--surface);
  padding: clamp(1rem, 4vw, 2rem);
  overflow: clip;
}

.lab-toolbar {
  display: flex;
  gap: 0.45rem;
  overflow-x: auto;
  padding: 0.15rem;
  scrollbar-width: thin;
}

.lab-chip {
  min-height: 2.75rem;
  flex: 0 0 auto;
  border: 1px solid var(--line);
  border-radius: 100vmax;
  background: var(--surface);
  color: var(--muted);
  padding: 0.52rem 0.8rem;
  font-size: 0.84rem;
  font-weight: 680;
  cursor: pointer;
}

.lab-chip:hover,
.lab-chip.is-active {
  border-color: var(--blue);
  background: var(--surface-blue);
  color: var(--blue-active);
}

.range-control {
  display: grid;
  gap: 0.65rem;
  margin-block: 1.6rem;
  color: var(--muted);
  font-size: 0.86rem;
}

.range-control strong {
  color: var(--ink-strong);
}

.range-control input {
  width: 100%;
  accent-color: var(--blue);
}

.composition-machine {
  display: grid;
  grid-template-columns: minmax(6rem, 0.7fr) auto minmax(8rem, 1fr) auto minmax(8rem, 1fr);
  gap: 0.6rem;
  align-items: center;
}

.machine-node {
  min-width: 0;
  min-height: 6.2rem;
  display: grid;
  place-content: center;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-md);
  background: var(--surface);
  padding: 0.75rem;
  text-align: center;
}

.machine-node span,
.rate-equation span,
.parts-map span {
  color: var(--muted);
  font-size: 0.7rem;
  font-weight: 680;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.machine-node strong {
  margin-top: 0.25rem;
  color: var(--ink-strong);
  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: 0.92rem;
  overflow-wrap: anywhere;
}

.machine-node .katex,
.rate-equation .katex,
.parts-map .katex {
  letter-spacing: normal;
  text-transform: none;
}

.input-node {
  background: var(--surface-blue);
}

.machine-arrow {
  color: var(--blue);
  font-weight: 800;
}

.rate-equation {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr) auto minmax(0, 1fr);
  gap: 0.65rem;
  align-items: center;
  margin-top: 1rem;
  border-radius: var(--radius-md);
  background: var(--surface-blue);
  padding: 1rem;
}

.rate-equation div {
  min-width: 0;
  text-align: center;
}

.rate-equation strong {
  display: block;
  color: var(--ink-strong);
  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: 0.78rem;
  overflow-wrap: anywhere;
}

.rate-total strong {
  color: var(--green);
  font-size: 1rem;
}

.lab-plot {
  margin: 1.4rem 0 0;
  border-top: 1px solid var(--line);
  padding-top: 1.15rem;
  overflow-x: auto;
  overscroll-behavior-x: contain;
}

.plot-heading {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.2rem 1rem;
  align-items: baseline;
}

.plot-heading strong {
  color: var(--ink-strong);
  font-size: 0.9rem;
}

.plot-heading span {
  color: var(--muted);
  font-size: 0.76rem;
}

.lab-plot svg {
  width: 100%;
  min-width: 30rem;
  height: auto;
  margin-top: 0.65rem;
  border-radius: var(--radius-sm);
  background: var(--surface);
}

.plot-grid line {
  stroke: var(--line);
  stroke-width: 1;
  vector-effect: non-scaling-stroke;
}

.plot-axes line {
  stroke: var(--faint);
  stroke-width: 1;
  vector-effect: non-scaling-stroke;
}

.plot-axes text {
  fill: var(--muted);
  font-family: Inter, ui-sans-serif, sans-serif;
  font-size: 11px;
}

.plot-curve {
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 2.5;
  vector-effect: non-scaling-stroke;
}

.plot-curve-function {
  stroke: var(--blue-hover);
}

.plot-curve-tangent {
  stroke: var(--ink-strong);
  stroke-dasharray: 7 5;
}

.plot-curve-check {
  stroke: var(--ink-strong);
  stroke-dasharray: 4 5;
}

.plot-point {
  fill: var(--surface);
  stroke: var(--blue-active);
  stroke-width: 3;
  vector-effect: non-scaling-stroke;
}

.lab-plot figcaption {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem 1rem;
  margin-top: 0.35rem;
  color: var(--muted);
  font-size: 0.72rem;
}

.plot-key {
  display: inline-flex;
  gap: 0.4rem;
  align-items: center;
}

.plot-key::before {
  width: 1.35rem;
  height: 2px;
  display: block;
  background: var(--blue-hover);
  content: "";
}

.plot-key-tangent::before,
.plot-key-check::before {
  height: 0;
  border-top: 2px dashed var(--ink-strong);
  background: none;
}

.verification-plot {
  margin-top: 1rem;
}

.lab-caption {
  margin: 1rem 0 0;
  color: var(--muted);
  font-size: 0.84rem;
}

.method-steps {
  display: grid;
  gap: 0;
  margin: 1.8rem 0 0;
  padding: 0;
  list-style: none;
}

.method-steps li {
  display: grid;
  grid-template-columns: 2.6rem minmax(0, 1fr);
  gap: 1rem;
  border-top: 1px solid var(--line);
  padding-block: 1.25rem;
}

.method-steps li > span {
  width: 2.25rem;
  height: 2.25rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-strong);
  color: var(--blue-active);
  font-weight: 800;
}

.method-steps h3 {
  margin: 0;
  font-size: 1.08rem;
}

.method-steps p {
  margin: 0.25rem 0 0;
  color: var(--muted);
  font-size: 0.92rem;
}

.decision-note {
  border-left: 3px solid var(--blue);
  background: var(--surface-blue);
  padding: 1rem 1.15rem;
}

.decision-note strong {
  color: var(--ink-strong);
}

.decision-note p {
  margin: 0.2rem 0 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.worked-example {
  border-top: 1px solid var(--line);
  padding-block: 2rem;
}

.worked-example:last-of-type {
  border-bottom: 1px solid var(--line);
}

.example-heading {
  display: grid;
  grid-template-columns: 5.5rem minmax(0, 1fr);
  gap: 1rem;
  align-items: baseline;
}

.example-heading > span {
  color: var(--blue-active);
  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: 0.75rem;
  font-weight: 760;
  text-transform: uppercase;
}

.example-heading h3 {
  margin: 0;
}

.worked-example > p,
.worked-example > ol,
.worked-example > .katex-display {
  margin-left: 6.5rem;
}

.worked-example p,
.worked-example li {
  color: var(--muted);
}

.example-check {
  border-radius: var(--radius-sm);
  background: var(--green-bg);
  padding: 0.75rem 0.9rem;
  color: var(--ink) !important;
  font-size: 0.88rem;
}

.example-check > span {
  color: var(--green);
  font-weight: 900;
}

.solver-callout {
  display: flex;
  justify-content: space-between;
  gap: 1.5rem;
  align-items: center;
  margin-top: 2rem;
  border-radius: var(--radius-md);
  background: var(--ink-strong);
  color: var(--surface);
  padding: 1.25rem;
}

.solver-callout strong {
  font-size: 1.08rem;
}

.solver-callout p {
  margin: 0.2rem 0 0;
  color: #e8edf2;
  font-size: 0.86rem;
}

.mistake-list {
  display: block;
  border-top: 1px solid var(--line);
}

.mistake-list article {
  border-bottom: 1px solid var(--line);
  padding-block: 1rem;
}

.mistake-list h3 {
  margin: 0;
  font-size: 1.02rem;
}

.mistake-list p {
  margin: 0.3rem 0 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.practice-list {
  border-top: 1px solid var(--line);
}

.practice-list details {
  border-bottom: 1px solid var(--line);
}

.practice-list summary {
  min-height: 3.75rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  color: var(--ink-strong);
  font-weight: 680;
  cursor: pointer;
  list-style: none;
}

.practice-list summary::-webkit-details-marker {
  display: none;
}

.practice-list summary::after {
  content: "Show answer";
  flex: 0 0 auto;
  color: var(--blue-active);
  font-size: 0.72rem;
  font-weight: 740;
}

.practice-list details[open] summary::after {
  content: "Hide answer";
}

.practice-list details > p {
  padding: 0 2rem 1rem 0;
  color: var(--muted);
}

.curriculum-note {
  border-left: 3px solid var(--blue);
  padding-left: clamp(1rem, 4vw, 2rem);
}

.sources h2 {
  font-size: 1.35rem;
}

.derivation-flow {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr) auto minmax(0, 1fr);
  gap: 0.55rem;
  align-items: stretch;
  margin-block: 1.5rem 2.5rem;
}

.derivation-flow > div {
  min-width: 0;
  display: grid;
  align-content: center;
  border: 0;
  border-bottom: 1px solid var(--line);
  border-radius: 0;
  background: var(--surface);
  padding: 0.8rem;
  text-align: center;
}

.derivation-flow > span {
  align-self: center;
  color: var(--blue);
  font-weight: 800;
}

.derivation-flow div > span {
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 760;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.derivation-flow .katex-display {
  margin: 0.6rem 0 0;
  font-size: 0.75rem;
}

.parts-question {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(11rem, 0.75fr);
  gap: 1.5rem;
  align-items: start;
  margin-block: 1.5rem 1rem;
  border-radius: var(--radius-md);
  background: var(--surface);
  padding: 1rem;
}

.parts-question strong {
  display: block;
  color: var(--ink-strong);
  font-size: 1.15rem;
}

.parts-question p {
  margin: 0.35rem 0 0;
  color: var(--muted);
  font-size: 0.86rem;
}

.parts-question fieldset {
  display: grid;
  gap: 0.35rem;
  margin: 0;
  border: 0;
  padding: 0;
}

.parts-question legend {
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 700;
}

.parts-question label {
  min-height: 2.75rem;
  display: flex;
  gap: 0.55rem;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: 0.45rem 0.65rem;
  cursor: pointer;
}

.parts-question input {
  accent-color: var(--blue);
}

.choice-feedback {
  min-height: 2.8rem;
  margin-top: 0.75rem;
  color: var(--muted);
  font-size: 0.86rem;
}

.parts-map {
  display: grid;
  grid-template-columns: minmax(0, 0.75fr) auto minmax(0, 0.9fr) auto minmax(0, 1.35fr);
  gap: 0.55rem;
  align-items: center;
  border-top: 1px solid var(--line-strong);
  padding-top: 1rem;
}

.parts-map[hidden] {
  display: none;
}

.parts-map > div {
  min-width: 0;
  border-radius: var(--radius-sm);
  background: var(--surface-blue);
  padding: 0.75rem;
  text-align: center;
}

.parts-map strong,
.parts-map small {
  display: block;
  overflow-wrap: anywhere;
}

.parts-map strong {
  color: var(--ink-strong);
  font-size: 0.84rem;
}

.parts-map small {
  margin-top: 0.25rem;
  color: var(--muted);
  font-size: 0.72rem;
}

@media (max-width: 820px) {
  .article-layout {
    grid-template-columns: 1fr;
    gap: 0;
  }

  .article-outline {
    display: none;
  }
}

@media (max-width: 650px) {
  .parts-question {
    grid-template-columns: 1fr;
  }

  .composition-machine,
  .rate-equation,
  .derivation-flow,
  .parts-map {
    grid-template-columns: 1fr;
  }

  .machine-arrow,
  .derivation-flow > span,
  .parts-map > span {
    justify-self: center;
    transform: rotate(90deg);
  }

  .machine-node {
    min-height: 5.2rem;
  }

  .rate-equation > span {
    justify-self: center;
  }

  .example-heading {
    grid-template-columns: 1fr;
    gap: 0.3rem;
  }

  .worked-example > p,
  .worked-example > ol,
  .worked-example > .katex-display {
    margin-left: 0;
  }

  .solver-callout {
    align-items: stretch;
    flex-direction: column;
  }

  .solver-callout .button {
    width: 100%;
  }

}