:root {
  color-scheme: light;
  --ink: #1b2a41;
  --ink-soft: #5a6b84;
  --wash: #f0f4f8;
  --wash-deep: #dce5ef;
  --accent: #0e7490;
  --accent-dark: #155e75;
  --surface: #ffffff;
  --line: rgba(27, 42, 65, 0.14);
  --font-display: "Fraunces", Georgia, serif;
  --font-body: "Nunito", "Trebuchet MS", sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-body);
  color: var(--ink);
  background:
    radial-gradient(ellipse 70% 45% at 15% 5%, rgba(14, 116, 144, 0.14), transparent 55%),
    radial-gradient(ellipse 55% 40% at 90% 75%, rgba(27, 42, 65, 0.08), transparent 50%),
    linear-gradient(180deg, var(--wash) 0%, var(--wash-deep) 100%);
}

.shell {
  max-width: 42rem;
  margin: 0 auto;
  padding: 2.25rem 1.35rem 3.5rem;
}

.intro {
  margin-bottom: 1.75rem;
  animation: rise-in 0.7s ease-out both;
}

.eyebrow {
  margin: 0 0 0.4rem;
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

h1 {
  margin: 0;
  font-family: var(--font-display);
  font-size: clamp(2.2rem, 6vw, 3.2rem);
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.05;
}

.lede {
  margin: 0.85rem 0 0;
  color: var(--ink-soft);
  line-height: 1.5;
}

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

.problem {
  padding: 1.5rem 1.45rem;
  border: 1px solid var(--line);
  border-radius: 1.15rem;
  background: var(--surface);
  box-shadow: 0 14px 36px rgba(27, 42, 65, 0.07);
  animation: rise-in 0.75s ease-out 0.08s both;
}

.story {
  margin: 0;
  font-size: clamp(1.15rem, 2.8vw, 1.35rem);
  line-height: 1.7;
}

.inline-field {
  display: inline-block;
  vertical-align: baseline;
  margin: 0 0.15rem;
}

.inline-field input {
  width: 4.25rem;
  padding: 0.25rem 0.4rem;
  border: 1.5px solid rgba(14, 116, 144, 0.35);
  border-radius: 0.5rem;
  background: rgba(14, 116, 144, 0.06);
  color: var(--ink);
  font: inherit;
  font-weight: 700;
  text-align: center;
}

.inline-field input:focus-visible {
  outline: 3px solid rgba(14, 116, 144, 0.35);
  outline-offset: 2px;
  border-color: var(--accent);
}

.value-legend {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
  margin: 1.35rem 0 0;
  padding: 0;
}

.value-legend div {
  margin: 0;
  padding: 0.75rem 0.85rem;
  border-radius: 0.75rem;
  background: var(--wash);
}

.value-legend dt {
  margin: 0;
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.value-legend dd {
  margin: 0.25rem 0 0;
  font-family: var(--font-display);
  font-size: 1.35rem;
  font-weight: 600;
}

.value-legend dd {
  margin: 0.25rem 0 0;
  font-family: var(--font-display);
  font-size: 1.35rem;
  font-weight: 600;
}

.work {
  margin-top: 1.35rem;
  padding: 1.35rem 1.45rem 1.5rem;
  border: 1px solid var(--line);
  border-radius: 1.15rem;
  background: var(--surface);
  box-shadow: 0 14px 36px rgba(27, 42, 65, 0.07);
  animation: rise-in 0.75s ease-out 0.12s both;
}

.work h2 {
  margin: 0 0 1rem;
  font-family: var(--font-display);
  font-size: 1.25rem;
  font-weight: 600;
}

.work-steps {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  align-items: start;
}

.arith-card {
  margin: 0;
  padding: 1rem 1.1rem;
  border-radius: 0.85rem;
  background: var(--wash);
}

.arith-card figcaption {
  margin: 0 0 0.75rem;
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.arith {
  margin: 0;
  font-family: "Courier New", Courier, monospace;
  font-size: clamp(1.15rem, 3.5vw, 1.45rem);
  font-weight: 700;
  line-height: 1.35;
  text-align: right;
  white-space: pre;
  color: var(--ink);
}

.arith-answer {
  display: block;
  margin-top: 0;
}

.answer-flash {
  display: inline-block;
  border-radius: 0.35rem;
  padding: 0 0.15rem;
  animation: answer-pop 0.85s ease-out;
}

.ld-quotient.answer-flash,
.ld-remainder.answer-flash {
  display: inline-block;
}

.ld-remainder {
  display: block;
  margin-top: 0.1rem;
}

.result-value.answer-flash {
  display: inline-block;
}

@keyframes answer-pop {
  0% {
    opacity: 0;
    transform: scale(0.92);
    background-color: rgba(14, 116, 144, 0.35);
    color: var(--accent-dark);
  }
  35% {
    opacity: 1;
    transform: scale(1.06);
    background-color: rgba(14, 116, 144, 0.28);
  }
  55% {
    transform: scale(1);
    background-color: rgba(14, 116, 144, 0.18);
  }
  100% {
    opacity: 1;
    transform: scale(1);
    background-color: transparent;
  }
}

.long-division {
  font-family: "Courier New", Courier, monospace;
  font-size: clamp(1.05rem, 3vw, 1.3rem);
  font-weight: 700;
  line-height: 1.35;
  color: var(--ink);
}

.long-division-grid {
  display: inline-grid;
  grid-template-columns: auto auto;
  column-gap: 0.15rem;
  justify-items: start;
}

.ld-quotient {
  grid-column: 2;
  padding-left: 0.55rem;
  letter-spacing: 0.08em;
}

.ld-rule {
  grid-column: 2;
  width: 100%;
  border-top: 2px solid var(--ink);
  margin: 0.1rem 0;
}

.ld-divisor {
  justify-self: end;
  padding-right: 0.2rem;
}

.ld-dividend-wrap {
  border-left: 2px solid var(--ink);
  padding-left: 0.55rem;
}

.ld-work {
  grid-column: 2;
  padding-left: 0.55rem;
  margin-top: 0.15rem;
  white-space: pre;
  text-align: right;
}

.ld-placeholder {
  margin: 0;
  font-family: var(--font-body);
  font-weight: 600;
  color: var(--ink-soft);
}

.arith-card-wide {
  grid-column: 1 / -1;
}

.round-work {
  display: grid;
  gap: 0.55rem;
  font-size: 1.05rem;
  line-height: 1.45;
}

.round-work p {
  margin: 0;
}

.round-work .round-start {
  font-family: "Courier New", Courier, monospace;
  font-size: 1.2rem;
  font-weight: 700;
}

.round-work .round-check {
  color: var(--ink-soft);
}

.round-work .round-answer {
  font-family: var(--font-display);
  font-size: 1.35rem;
  font-weight: 600;
  color: var(--accent-dark);
}

.round-placeholder {
  margin: 0;
  color: var(--ink-soft);
  font-weight: 600;
}

.result {
  margin-top: 1.35rem;
  padding: 1.5rem 1.45rem;
  border: 1px solid var(--line);
  border-radius: 1.15rem;
  background: var(--surface);
  text-align: center;
  box-shadow: 0 14px 36px rgba(27, 42, 65, 0.07);
  animation: rise-in 0.75s ease-out 0.16s both;
}

.result-label {
  margin: 0;
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--ink-soft);
}

.result-value {
  margin: 0.4rem 0 0;
  font-family: var(--font-display);
  font-size: clamp(3rem, 10vw, 4.5rem);
  font-weight: 700;
  line-height: 1;
  color: var(--accent-dark);
}

.result-note {
  margin: 0.75rem 0 0;
  min-height: 1.4em;
  color: var(--ink-soft);
  line-height: 1.4;
}

.result-note.is-error {
  color: #a33b2a;
  font-weight: 600;
}

@media (max-width: 520px) {
  .shell {
    padding: 1.5rem 1rem 2.75rem;
  }

  .value-legend {
    grid-template-columns: 1fr;
  }

  .work-steps {
    grid-template-columns: 1fr;
  }

  .arith-card-wide {
    grid-column: auto;
  }

  .inline-field input {
    width: 3.75rem;
  }
}

@keyframes rise-in {
  from {
    opacity: 0;
    transform: translateY(0.85rem);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (prefers-reduced-motion: reduce) {
  .intro,
  .problem,
  .work,
  .result,
  .answer-flash {
    animation: none !important;
  }
}