:root {
  --bg0: #f7f2e6;
  --bg1: #efe5cf;
  --ink: #0b1220;
  --muted: rgba(11, 18, 32, 0.74);
  --card: rgba(255, 255, 255, 0.72);
  --cardSolid: #ffffff;
  --stroke: rgba(11, 18, 32, 0.14);
  --stroke2: rgba(11, 18, 32, 0.08);
  --accent: #0f766e;
  --gold: #b45309;
  --bad: #b91c1c;
  --good: #0f766e;
  --shadow: 0 18px 45px rgba(11, 18, 32, 0.18);
  --shadow2: 0 12px 26px rgba(11, 18, 32, 0.14);
  --radius-xl: 28px;
  --radius-lg: 22px;
  --radius-md: 16px;
  --radius-sm: 12px;
  --max: 1120px;
  --pad: clamp(18px, 3vw, 34px);
}

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

html,
body {
  height: 100%;
}

body {
  margin: 0;
  color: var(--ink);
  font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  line-height: 1.35;
  background:
    radial-gradient(1000px 700px at 12% 10%, rgba(15, 118, 110, 0.18), transparent 56%),
    radial-gradient(900px 640px at 80% 12%, rgba(180, 83, 9, 0.16), transparent 52%),
    radial-gradient(900px 620px at 54% 92%, rgba(2, 132, 199, 0.12), transparent 55%),
    linear-gradient(180deg, var(--bg0), var(--bg1));
  background-attachment: fixed;
}

@media (prefers-reduced-motion: reduce) {
  body {
    background-attachment: scroll;
  }
}

a {
  color: inherit;
  text-decoration-color: rgba(11, 18, 32, 0.28);
  text-underline-offset: 3px;
}

a:hover {
  text-decoration-color: rgba(11, 18, 32, 0.55);
}

code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  font-size: 0.92em;
  background: rgba(11, 18, 32, 0.06);
  border: 1px solid rgba(11, 18, 32, 0.10);
  padding: 2px 6px;
  border-radius: 10px;
}

.skip-link {
  position: absolute;
  left: 12px;
  top: 10px;
  z-index: 9999;
  padding: 10px 12px;
  background: var(--cardSolid);
  border: 1px solid var(--stroke);
  border-radius: 12px;
  transform: translateY(-130%);
  transition: transform 160ms ease;
}

.skip-link:focus {
  transform: translateY(0);
  outline: none;
}

.site-header {
  padding: 10px 0 0;
}

.nav {
  width: min(var(--max), calc(100% - var(--pad) * 2));
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 14px;
  padding: 10px 12px;
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.55);
  border: 1px solid rgba(11, 18, 32, 0.10);
  backdrop-filter: blur(10px);
  position: sticky;
  top: 10px;
  z-index: 50;
}

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

.brand-mark {
  width: 38px;
  height: 38px;
  display: grid;
  place-items: center;
  border-radius: 14px;
  background: linear-gradient(135deg, rgba(15, 118, 110, 0.18), rgba(180, 83, 9, 0.15));
  border: 1px solid rgba(11, 18, 32, 0.10);
  font-weight: 700;
  letter-spacing: 0.5px;
}

.brand-text {
  font-weight: 700;
  letter-spacing: 0.2px;
}

.nav-links {
  display: flex;
  gap: 18px;
  justify-content: center;
  font-weight: 600;
}

.nav-links a {
  text-decoration: none;
  padding: 10px 10px;
  border-radius: 999px;
}

.nav-links a:hover {
  background: rgba(15, 118, 110, 0.10);
}

.nav-actions {
  display: flex;
  gap: 10px;
  justify-content: end;
}

.chip {
  border: 1px solid rgba(11, 18, 32, 0.14);
  background: rgba(255, 255, 255, 0.72);
  border-radius: 999px;
  padding: 9px 12px;
  font-weight: 600;
  cursor: pointer;
}

.chip[aria-pressed="true"] {
  border-color: rgba(15, 118, 110, 0.45);
  box-shadow: 0 0 0 3px rgba(15, 118, 110, 0.12);
}

.chip:hover {
  background: rgba(255, 255, 255, 0.92);
}

.hero {
  width: min(var(--max), calc(100% - var(--pad) * 2));
  margin: 26px auto 0;
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 26px;
  align-items: center;
  padding: clamp(18px, 4vw, 38px);
  border-radius: var(--radius-xl);
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.65), rgba(255, 255, 255, 0.50));
  border: 1px solid rgba(11, 18, 32, 0.12);
  box-shadow: var(--shadow);
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: "";
  position: absolute;
  inset: -80px;
  background:
    radial-gradient(closest-side at 28% 20%, rgba(15, 118, 110, 0.18), transparent 70%),
    radial-gradient(closest-side at 70% 30%, rgba(180, 83, 9, 0.16), transparent 72%),
    radial-gradient(closest-side at 50% 90%, rgba(2, 132, 199, 0.10), transparent 72%);
  filter: blur(8px);
  pointer-events: none;
}

.hero-copy,
.hero-visual {
  position: relative;
}

h1,
h2 {
  font-family: ui-serif, Georgia, "Times New Roman", serif;
  letter-spacing: -0.4px;
}

h1 {
  font-size: clamp(34px, 4.4vw, 56px);
  line-height: 0.98;
  margin: 0 0 12px;
}

.lead {
  font-size: clamp(16px, 2.0vw, 20px);
  color: var(--muted);
  max-width: 52ch;
  margin: 0 0 18px;
}

.hero-cta {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin: 12px 0 18px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  padding: 12px 14px;
  border-radius: 16px;
  border: 1px solid rgba(11, 18, 32, 0.14);
  background: rgba(255, 255, 255, 0.86);
  box-shadow: 0 8px 16px rgba(11, 18, 32, 0.10);
  cursor: pointer;
  text-decoration: none;
  font-weight: 700;
  transition: transform 120ms ease, box-shadow 120ms ease, background 120ms ease;
}

.btn:hover {
  transform: translateY(-1px);
  background: rgba(255, 255, 255, 0.96);
  box-shadow: 0 10px 18px rgba(11, 18, 32, 0.12);
}

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

.btn.primary {
  border-color: rgba(15, 118, 110, 0.35);
  background: linear-gradient(135deg, rgba(15, 118, 110, 0.18), rgba(180, 83, 9, 0.12));
}

.btn.ghost {
  background: transparent;
  box-shadow: none;
}

.btn:focus-visible,
.chip:focus-visible,
input:focus-visible,
select:focus-visible,
.cmp-btn:focus-visible {
  outline: none;
  box-shadow: 0 0 0 4px rgba(15, 118, 110, 0.18);
}

.hero-stats {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
}

.stat {
  min-width: 118px;
  padding: 12px 14px;
  border-radius: 18px;
  border: 1px solid rgba(11, 18, 32, 0.10);
  background: rgba(255, 255, 255, 0.56);
}

.stat-number {
  font-size: 24px;
  font-weight: 800;
}

.stat-label {
  color: rgba(11, 18, 32, 0.66);
  font-weight: 650;
}

.hero-visual {
  display: grid;
  gap: 12px;
  justify-items: center;
}

.hero-svg {
  width: min(420px, 100%);
  height: auto;
}

.hero-scribble {
  font-family: ui-serif, Georgia, "Times New Roman", serif;
  font-size: 22px;
  fill: rgba(11, 18, 32, 0.70);
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border-radius: 999px;
  border: 1px solid rgba(11, 18, 32, 0.12);
  background: rgba(255, 255, 255, 0.66);
  font-weight: 700;
}

.badge-dot {
  width: 10px;
  height: 10px;
  border-radius: 999px;
  background: var(--accent);
  box-shadow: 0 0 0 5px rgba(15, 118, 110, 0.14);
}

main {
  width: min(var(--max), calc(100% - var(--pad) * 2));
  margin: 28px auto 0;
  padding-bottom: 46px;
}

.panel {
  margin-top: 18px;
  padding: clamp(18px, 3vw, 28px);
  border-radius: var(--radius-xl);
  border: 1px solid rgba(11, 18, 32, 0.12);
  background: rgba(255, 255, 255, 0.45);
  box-shadow: var(--shadow2);
}

.panel-head {
  margin-bottom: 14px;
}

h2 {
  margin: 0 0 6px;
  font-size: clamp(26px, 2.8vw, 36px);
}

.panel-sub {
  margin: 0;
  color: rgba(11, 18, 32, 0.74);
  max-width: 70ch;
}

.grid-2 {
  margin-top: 16px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}

.card {
  padding: 16px 16px 14px;
  border-radius: var(--radius-lg);
  border: 1px solid rgba(11, 18, 32, 0.12);
  background: var(--card);
  backdrop-filter: blur(10px);
}

.card-title-row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 10px;
}

.card-title {
  margin: 0;
  font-size: 18px;
  letter-spacing: -0.2px;
}

.linkish {
  border: none;
  background: none;
  padding: 6px 8px;
  border-radius: 12px;
  font-weight: 800;
  cursor: pointer;
  text-decoration: underline;
  text-decoration-color: rgba(11, 18, 32, 0.28);
}

.linkish:hover {
  background: rgba(15, 118, 110, 0.10);
  text-decoration-color: rgba(11, 18, 32, 0.55);
}

.prompt {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: clamp(10px, 2vw, 18px);
  padding: 12px 8px;
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.50);
  border: 1px solid rgba(11, 18, 32, 0.08);
}

.fraction {
  display: inline-grid;
  grid-template-rows: auto 2px auto;
  align-items: center;
  justify-items: center;
  min-width: 56px;
}

.fraction .bar {
  width: 100%;
  height: 2px;
  background: rgba(11, 18, 32, 0.30);
  border-radius: 999px;
}

.fraction.big {
  min-width: 78px;
  font-size: 24px;
}

.fraction input {
  width: 64px;
  font: inherit;
  text-align: center;
  border-radius: 12px;
  border: 1px solid rgba(11, 18, 32, 0.16);
  background: rgba(255, 255, 255, 0.90);
  padding: 8px 8px;
  font-weight: 800;
  color: var(--ink);
}

.op {
  display: grid;
  justify-items: center;
  gap: 8px;
  min-width: 72px;
  font-weight: 900;
}

.pill {
  display: inline-block;
  padding: 6px 10px;
  border-radius: 999px;
  background: linear-gradient(135deg, rgba(15, 118, 110, 0.16), rgba(180, 83, 9, 0.12));
  border: 1px solid rgba(11, 18, 32, 0.10);
  font-weight: 900;
}

.arrow {
  font-size: 22px;
  font-weight: 900;
  color: rgba(11, 18, 32, 0.64);
}

.op-sign {
  font-size: 26px;
  font-weight: 900;
  color: rgba(11, 18, 32, 0.72);
  min-width: 32px;
  text-align: center;
}

.addsub-level-row {
  margin-bottom: 10px;
}

.addsub-level-row select {
  min-width: 210px;
}

.actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  margin-top: 12px;
}

.feedback {
  margin-top: 10px;
  padding: 10px 12px;
  border-radius: 16px;
  border: 1px solid rgba(11, 18, 32, 0.10);
  background: rgba(255, 255, 255, 0.58);
  min-height: 44px;
  color: rgba(11, 18, 32, 0.80);
  font-weight: 650;
}

.feedback.good {
  border-color: rgba(15, 118, 110, 0.25);
  box-shadow: 0 0 0 4px rgba(15, 118, 110, 0.10);
}

.feedback.bad {
  border-color: rgba(185, 28, 28, 0.25);
  box-shadow: 0 0 0 4px rgba(185, 28, 28, 0.08);
}

.steps {
  margin-top: 10px;
  padding: 12px 12px;
  border-radius: 16px;
  border: 1px dashed rgba(11, 18, 32, 0.20);
  background: rgba(255, 255, 255, 0.44);
  font-weight: 650;
}

.model-card .model-shelf {
  display: grid;
  gap: 12px;
}

.model-block {
  display: grid;
  gap: 8px;
  padding: 12px 12px;
  border-radius: 18px;
  border: 1px solid rgba(11, 18, 32, 0.10);
  background: rgba(255, 255, 255, 0.52);
}

.model-label {
  font-weight: 850;
  color: rgba(11, 18, 32, 0.74);
}

.model-note {
  margin: 10px 0 0;
  color: rgba(11, 18, 32, 0.70);
}

.model-placeholder {
  padding: 10px 12px;
  border-radius: 14px;
  border: 1px dashed rgba(11, 18, 32, 0.20);
  background: rgba(255, 255, 255, 0.38);
  color: rgba(11, 18, 32, 0.72);
  font-weight: 750;
  text-align: center;
}

.tape {
  width: 100%;
  height: auto;
}

.tape-bg {
  fill: rgba(255, 255, 255, 0.55);
  stroke: rgba(11, 18, 32, 0.16);
  stroke-width: 2;
}

.tape-part {
  fill: transparent;
  stroke: rgba(11, 18, 32, 0.14);
  stroke-width: 2;
}

.tape-fill {
  fill: rgba(15, 118, 110, 0.28);
  stroke: rgba(15, 118, 110, 0.28);
  stroke-width: 2;
}

.compare-row {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 12px;
  padding: 10px 8px;
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.50);
  border: 1px solid rgba(11, 18, 32, 0.08);
}

.compare-buttons {
  display: grid;
  gap: 8px;
}

.cmp-btn {
  width: 52px;
  height: 44px;
  border-radius: 16px;
  border: 1px solid rgba(11, 18, 32, 0.14);
  background: rgba(255, 255, 255, 0.74);
  font-weight: 900;
  font-size: 18px;
  cursor: pointer;
}

.cmp-btn:hover {
  background: rgba(255, 255, 255, 0.95);
}

.cmp-btn.is-picked {
  border-color: rgba(15, 118, 110, 0.40);
  box-shadow: 0 0 0 4px rgba(15, 118, 110, 0.12);
}

.ws-form {
  display: grid;
  gap: 10px;
}

.ws-row {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  align-items: end;
}

label {
  display: grid;
  gap: 6px;
  font-weight: 800;
  color: rgba(11, 18, 32, 0.78);
}

input[type="number"],
select {
  border: 1px solid rgba(11, 18, 32, 0.16);
  border-radius: 14px;
  padding: 10px 12px;
  background: rgba(255, 255, 255, 0.90);
  font: inherit;
  font-weight: 650;
}

.ws-check {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border-radius: 16px;
  border: 1px solid rgba(11, 18, 32, 0.12);
  background: rgba(255, 255, 255, 0.52);
}

.ws-check input {
  width: 18px;
  height: 18px;
}

.quiz-score {
  font-weight: 900;
  color: rgba(11, 18, 32, 0.70);
}

.quiz-stage {
  display: grid;
  gap: 12px;
  margin-top: 10px;
}

.quiz-promptline {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: space-between;
  align-items: baseline;
  padding: 8px 2px 2px;
  color: rgba(11, 18, 32, 0.72);
  font-weight: 850;
}

.quiz-choices {
  display: flex;
  gap: 10px;
  justify-content: center;
  flex-wrap: wrap;
}

.quiz-actions {
  justify-content: space-between;
}

.tiny {
  margin: 2px 0 0;
  color: rgba(11, 18, 32, 0.64);
}

.site-footer {
  width: min(var(--max), calc(100% - var(--pad) * 2));
  margin: 0 auto 40px;
}

.footer-inner {
  display: flex;
  gap: 18px;
  justify-content: space-between;
  align-items: start;
  padding: 16px 18px;
  border-radius: var(--radius-xl);
  border: 1px solid rgba(11, 18, 32, 0.12);
  background: rgba(255, 255, 255, 0.52);
}

.footer-title {
  font-weight: 900;
}

.footer-note {
  color: rgba(11, 18, 32, 0.70);
  max-width: 60ch;
}

.footer-links {
  display: flex;
  gap: 12px;
  font-weight: 800;
}

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

.reveal [data-reveal] {
  opacity: 1;
  transform: translateY(0);
  transition: opacity 420ms ease, transform 420ms ease;
}

.reveal [data-reveal].is-hidden {
  opacity: 0;
  transform: translateY(8px);
}

/* The reveal transform must not contribute horizontal scroll on narrow screens. */
html,
body {
  max-width: 100%;
  overflow-x: hidden;
}

.reveal [data-reveal].is-visible {
  opacity: 1;
  transform: translateY(0);
}

body.is-focus .nav-links,
body.is-focus .hero-visual,
body.is-focus .site-footer,
body.is-focus #worksheet {
  display: none !important;
}

body.is-focus .hero {
  grid-template-columns: 1fr;
}

body.is-focus main {
  margin-top: 12px;
}

@media (max-width: 920px) {
  .nav {
    grid-template-columns: 1fr auto;
    grid-template-areas:
      "brand actions"
      "links links";
  }

  .brand {
    grid-area: brand;
  }

  .nav-actions {
    grid-area: actions;
  }

  .nav-links {
    grid-area: links;
    justify-content: start;
    flex-wrap: wrap;
  }

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

  .grid-2 {
    grid-template-columns: 1fr;
  }
}

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

@media print {
  .reveal [data-reveal].is-hidden {
    opacity: 1 !important;
    transform: none !important;
  }
}