:root {
  color-scheme: light;
  --ink: #1d2a26;
  --muted: #5d6b66;
  --bg: #efeae2;
  --card: #ffffff;
  --line: #eadfce;
  --accent: #1f6f5b;
  --accent-dark: #164f42;
  --pink: #ffdef7;
  --pink-edge: #e7a8d4;
  --green: #157a34;
  --red: #c62828;
  --mark: #ffe08a;
  --shadow: 0 14px 40px rgba(40, 32, 24, 0.12);
  --col-gap: 1.05rem;
  --step-gap: 0.85rem;
  --chain-gap: 0.55rem;
  --input-h: 2.65rem;
  --input-w: 5.2rem;
  --carry-w: 4.4rem;
  --op-size: 1.05rem;
  --board-pad: 0.15rem;
  font-family: "Segoe UI", "Helvetica Neue", system-ui, sans-serif;
}

* { box-sizing: border-box; }

html, body { height: 100%; }

body {
  margin: 0;
  height: 100dvh;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  color: var(--ink);
  background: radial-gradient(circle at top, #f7f4ee 0, var(--bg) 42%);
}

.site-header {
  display: flex;
  justify-content: center;
  flex: 0 0 auto;
  padding: 0.45rem 0.75rem 0;
}

.wordmark {
  margin: 0;
  display: flex;
  align-items: baseline;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.55rem;
  font-weight: 800;
  text-align: center;
  color: var(--accent);
}

.wordmark-name {
  font-size: clamp(2.4rem, 7vw, 4rem);
  letter-spacing: 0.04em;
  line-height: 0.95;
}

.wordmark-tag {
  font-size: clamp(1.15rem, 3.2vw, 1.85rem);
  letter-spacing: 0.01em;
}

main {
  flex: 1;
  min-height: 0;
  width: min(1280px, calc(100% - 1rem));
  margin: 0 auto;
  display: flex;
  flex-direction: column;
}

.panel {
  margin-top: 0.45rem;
  padding: clamp(0.7rem, 1.6vw, 1.15rem);
  background: var(--card);
  border-radius: 1rem;
  box-shadow: var(--shadow);
}

#setup {
  overflow: auto;
}

#exercise:not([hidden]) {
  flex: 1;
  min-height: 0;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

h1 {
  margin: 0 0 0.3rem;
  font-size: clamp(1.25rem, 2.4vw, 1.6rem);
}

.lead,
.instruction,
.hint,
.task-label {
  color: var(--muted);
  line-height: 1.4;
}

.lead { margin-top: 0; }

fieldset {
  margin: 0.75rem 0;
  padding: 0;
  border: 0;
}

legend {
  padding: 0;
  margin-bottom: 0.4rem;
  font-weight: 700;
}

.choices {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
}

.choice,
.primary,
.secondary {
  font: inherit;
  cursor: pointer;
  border-radius: 0.65rem;
  min-height: 2.5rem;
  touch-action: manipulation;
}

.choice {
  min-width: 2.5rem;
  padding: 0.35rem 0.7rem;
  border: 1px solid #d5d0c8;
  background: #fff;
  color: var(--ink);
}

.choice.is-selected {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

.choices-ops .choice { flex: 1 1 8rem; }

.hint { margin: 0.45rem 0 0; }

.primary,
.secondary {
  border: 0;
  padding: 0.6rem 1rem;
}

.primary {
  background: var(--accent);
  color: #fff;
  font-weight: 700;
}

.primary:hover,
.primary:focus-visible { background: var(--accent-dark); }

.install {
  margin-top: 0.65rem;
}

#ios-install { margin-top: 0.75rem; }

.secondary {
  background: transparent;
  color: var(--accent-dark);
  border: 1px solid #c9d5d0;
}

.choice:focus-visible,
.primary:focus-visible,
.secondary:focus-visible,
input:focus-visible {
  outline: 3px solid #8fd0bf;
  outline-offset: 2px;
}

.task-label {
  margin: 0;
  font-weight: 700;
  color: var(--ink);
  flex-shrink: 0;
}

.instruction {
  margin: 0.2rem 0 0.35rem;
  flex-shrink: 0;
}

.board {
  --col-gap: 0.85rem;
  --step-gap: 0.7rem;
  --chain-gap: 0.55rem;
  --input-h: 2.65rem;
  --op-size: 1.05rem;
  flex: 0 1 auto;
  min-height: 0;
  overflow: auto;
  padding: 0.15rem 0 0.25rem;
}

.board[data-density="compact"] {
  --col-gap: 0.65rem;
  --step-gap: 0.45rem;
  --chain-gap: 0.32rem;
  --input-h: 2.25rem;
  --op-size: 0.95rem;
}

.board[data-density="tight"] {
  --col-gap: 0.45rem;
  --step-gap: 0.3rem;
  --chain-gap: 0.18rem;
  --input-h: 1.95rem;
  --op-size: 0.86rem;
}

.chain {
  display: flex;
  flex-direction: column;
  gap: var(--chain-gap);
  width: 100%;
}

.row {
  display: flex;
  align-items: center;
  gap: var(--step-gap);
  width: 100%;
}

.probe {
  position: absolute;
  visibility: hidden;
  pointer-events: none;
  left: 0;
  top: 0;
}

.carry {
  flex: 0 0 auto;
  min-width: var(--carry-w);
  padding: 0 0.45rem 0 0.15rem;
  font-weight: 800;
  font-size: var(--op-size);
  font-variant-numeric: tabular-nums;
  text-align: right;
}

.carry.is-waiting { color: transparent; }

.step {
  display: flex;
  align-items: center;
  gap: var(--col-gap);
  flex: 0 0 var(--step-w, auto);
  width: var(--step-w, auto);
  min-width: max-content;
  padding: 0.08rem 0.15rem 0.08rem 0.45rem;
  border-radius: 0.45rem;
}

.probe .step {
  flex: none;
  width: max-content;
}

.probe .op { margin-right: 0; }

.op {
  margin-right: auto;
  font-size: var(--op-size);
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  text-align: right;
  white-space: nowrap;
}

.link-arrow {
  width: 1.7rem;
  height: 0.85rem;
  flex: 0 0 auto;
  color: #8d9a94;
}

.answer {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  flex: 0 0 auto;
}

input {
  width: var(--input-w);
  height: var(--input-h);
  padding: 0 0.35rem;
  border: 1px solid #cfc8be;
  border-radius: 0.4rem;
  font: inherit;
  font-size: var(--op-size);
  font-variant-numeric: tabular-nums;
  text-align: center;
  background: #fff;
}

.step.is-active input {
  background: var(--pink);
  border-color: var(--pink-edge);
}

.step.is-wrong input { border-color: var(--red); }

.step.is-correct input { color: var(--ink); }

.status {
  width: 1.35rem;
  height: 1.35rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  flex: 0 0 auto;
}

.status svg,
.link-arrow svg {
  width: 100%;
  height: 100%;
  display: block;
}

.status.is-correct { color: var(--green); }
.status.is-wrong { color: var(--red); }

.chain.is-done .step.is-marked,
.chain.is-done .carry.is-marked {
  background: var(--mark);
}

.meters {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem 1.2rem;
  margin: 0.35rem 0 0;
  padding-top: 0.45rem;
  border-top: 1px solid var(--line);
  flex: 0 0 auto;
}

.meters p { margin: 0; }

.summary {
  margin: 0.45rem 0 0;
  padding: 0.55rem 0.75rem;
  border-radius: 0.7rem;
  background: #f4fbf7;
  line-height: 1.4;
  flex: 0 0 auto;
}

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.55rem;
  flex: 0 0 auto;
}

@media (prefers-reduced-motion: no-preference) {
  .step.is-wrong .answer { animation: shake 0.18s linear; }
}

@keyframes shake {
  25% { transform: translateX(-3px); }
  75% { transform: translateX(3px); }
}

@media (max-width: 720px) {
  .choices-ops .choice { flex-basis: calc(50% - 0.4rem); }
}

@media (max-height: 760px) {
  .site-header { padding-top: 0.25rem; }
  .wordmark-name { font-size: 2rem; }
  .wordmark-tag { font-size: 1.15rem; }
  .panel { margin-top: 0.3rem; padding: 0.65rem 0.75rem; }
  h1 { font-size: 1.2rem; }
  .lead { font-size: 0.92rem; }
  fieldset { margin: 0.45rem 0; }
  .choice, .primary, .secondary { min-height: 2.2rem; }
}