:root {
  color-scheme: light;
  --paper: #f7f2e7;
  --ink: #25211b;
  --muted: #766f64;
  --line: #d9cdb8;
  --wood: #8b4f2f;
  --wood-dark: #4e2d1f;
  --jade: #24756a;
  --jade-soft: #d7ebe6;
  --lacquer: #b83235;
  --gold: #d99a2b;
  --shadow: 0 18px 48px rgba(64, 39, 20, 0.16);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    linear-gradient(90deg, rgba(37, 33, 27, 0.04) 1px, transparent 1px) 0 0 / 36px 36px,
    linear-gradient(0deg, rgba(37, 33, 27, 0.035) 1px, transparent 1px) 0 0 / 36px 36px,
    var(--paper);
  color: var(--ink);
  font-family: "Microsoft YaHei", "PingFang SC", "Segoe UI", sans-serif;
}

button,
select {
  font: inherit;
}

.app {
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
  padding: 28px 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr) 380px;
  gap: 20px;
}

.play-area,
.history-panel {
  background: rgba(255, 252, 244, 0.86);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}

.play-area {
  min-width: 0;
  padding: 24px;
}

.history-panel {
  max-height: calc(100vh - 56px);
  padding: 20px;
  display: flex;
  flex-direction: column;
}

.topbar,
.history-header,
.status-strip,
.controls,
.legend {
  display: flex;
  align-items: center;
  gap: 14px;
}

.topbar,
.history-header {
  justify-content: space-between;
}

.eyebrow {
  margin: 0 0 4px;
  color: var(--jade);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

h1,
h2 {
  margin: 0;
  font-family: Georgia, "Songti SC", serif;
  font-weight: 700;
}

h1 {
  display: inline-flex;
  align-items: center;
  flex-wrap: nowrap;
  gap: 0.03em;
  font-size: clamp(40px, 8vw, 88px);
  line-height: 0.95;
  white-space: nowrap;
}

h1 > span {
  display: inline-block;
}

.title-ring {
  position: relative;
  display: inline-grid;
  place-items: center;
  width: 1.04em;
  height: 1.04em;
  margin-left: 0.02em;
  transform: translateY(0.03em) rotate(-5deg);
  border: 0.06em solid var(--lacquer);
  border-radius: 50%;
  background:
    radial-gradient(circle, rgba(255, 250, 240, 0.88) 0 54%, transparent 55%),
    linear-gradient(135deg, rgba(36, 117, 106, 0.12), rgba(217, 154, 43, 0.18));
  color: var(--lacquer);
  box-shadow: inset 0 0 0 0.04em rgba(184, 50, 53, 0.28), 0 0.09em 0 rgba(78, 45, 31, 0.12);
  font-size: 0.9em;
  line-height: 1;
}

.title-ring::after {
  content: "";
  position: absolute;
  inset: 0.12em;
  border: 0.025em solid rgba(184, 50, 53, 0.55);
  border-radius: 50%;
  pointer-events: none;
}

h2 {
  font-size: 26px;
}

.controls {
  align-items: flex-end;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.field {
  display: grid;
  gap: 6px;
  color: var(--muted);
  font-size: 13px;
}

select,
.hint-button,
.reset-button {
  min-height: 42px;
  border: 1px solid var(--wood);
  border-radius: 4px;
}

select {
  padding: 0 34px 0 12px;
  background: #fffaf0;
  color: var(--ink);
}

.hint-button,
.reset-button {
  cursor: pointer;
  padding: 0 16px;
  font-weight: 700;
}

.hint-button {
  background: #fffaf0;
  color: var(--wood-dark);
}

.hint-button:hover {
  background: #f2e4cd;
}

.hint-button:disabled {
  cursor: not-allowed;
  opacity: 0.55;
}

.reset-button {
  background: var(--wood);
  color: #fff7ea;
}

.reset-button:hover {
  background: var(--wood-dark);
}

.status-strip {
  margin: 24px 0 18px;
  padding: 12px 14px;
  justify-content: space-between;
  border-top: 3px solid var(--wood);
  border-bottom: 1px solid var(--line);
  background: #fffaf0;
}

.status-strip > div {
  display: grid;
  gap: 4px;
  min-width: 0;
}

.label {
  color: var(--muted);
  font-size: 12px;
}

.status-strip strong,
.status-strip code {
  font-size: 22px;
}

code {
  color: var(--lacquer);
  font-family: "Cascadia Mono", "Consolas", monospace;
}

.rings-stage {
  position: relative;
  min-height: 420px;
  padding: 38px 10px 28px;
  overflow: hidden;
  --rings-flow-top: 38px;
  --rod-top: 86px;
  --rod-height: 20px;
  --loop-width: 70px;
  --loop-height: 82px;
  --mounted-loop-top: calc(var(--rod-top) + (var(--rod-height) / 2) - (var(--loop-height) / 2) - var(--rings-flow-top));
}

.spine {
  position: absolute;
  left: 5%;
  right: 5%;
  top: var(--rod-top);
  height: var(--rod-height);
  border-radius: 999px;
  background: linear-gradient(180deg, #c99a61, var(--wood));
  box-shadow: inset 0 3px 0 rgba(255, 255, 255, 0.32), inset 0 -5px 0 rgba(0, 0, 0, 0.16);
  z-index: 1;
}

.spine::before,
.spine::after {
  content: "";
  position: absolute;
  top: 50%;
  width: 18px;
  height: 34px;
  transform: translateY(-50%);
  border-radius: 999px;
  background: linear-gradient(90deg, var(--wood-dark), var(--wood));
}

.spine::before {
  left: -10px;
}

.spine::after {
  right: -10px;
}

.rings {
  position: relative;
  display: grid;
  grid-template-columns: repeat(9, minmax(54px, 1fr));
  gap: 9px;
  align-items: start;
}

.ring {
  position: relative;
  height: 310px;
  border: 0;
  background: transparent;
  color: var(--ink);
  cursor: default;
  --loop-top: var(--mounted-loop-top);
}

.ring:disabled {
  cursor: default;
}

.ring:disabled .ring-label,
.ring:disabled .neighbor-link,
.ring:disabled .pin-foot {
  opacity: 0.52;
}

.ring.is-legal {
  cursor: pointer;
  opacity: 1;
}

.ring-loop {
  position: absolute;
  left: 50%;
  top: var(--loop-top);
  width: min(var(--loop-width), 92%);
  height: var(--loop-height);
  aspect-ratio: 1 / 1.18;
  transform: translateX(-50%);
  border: 9px solid var(--jade);
  border-radius: 50%;
  background: transparent;
  transition: top 180ms ease, transform 180ms ease, box-shadow 180ms ease;
}

.ring-loop-back {
  box-shadow: inset 0 -5px 0 rgba(0, 0, 0, 0.12), 0 10px 20px rgba(36, 117, 106, 0.2);
  -webkit-mask-image: linear-gradient(90deg, transparent 0 50%, #000 50% 100%);
  mask-image: linear-gradient(90deg, transparent 0 50%, #000 50% 100%);
  z-index: 0;
}

.ring-loop-front {
  box-shadow: inset 3px -4px 0 rgba(0, 0, 0, 0.1);
  -webkit-mask-image: linear-gradient(90deg, #000 0 51%, transparent 51% 100%);
  mask-image: linear-gradient(90deg, #000 0 51%, transparent 51% 100%);
  z-index: 3;
}

.ring-label {
  position: absolute;
  left: 50%;
  top: 0;
  z-index: 5;
  display: grid;
  place-items: center;
  width: 30px;
  height: 24px;
  transform: translateX(-50%);
  border-radius: 999px;
  background: #fffaf0;
  color: var(--ink);
  box-shadow: 0 2px 8px rgba(64, 39, 20, 0.12);
  font-weight: 700;
}

.neighbor-link {
  position: absolute;
  left: -17px;
  top: calc(var(--loop-top) + 72px);
  width: 34px;
  height: 10px;
  border-radius: 999px;
  background: linear-gradient(180deg, #f6cf83, var(--gold) 58%, #8f5f19);
  box-shadow: 0 3px 6px rgba(64, 39, 20, 0.18), inset 0 2px 0 rgba(255, 255, 255, 0.34);
  transform: rotate(0deg);
  z-index: 2;
}

.ring-pin {
  position: absolute;
  left: 50%;
  top: calc(var(--loop-top) + var(--loop-height) - 8px);
  width: 10px;
  height: calc(296px - var(--loop-top) - var(--loop-height));
  transform: translateX(-50%);
  border-radius: 999px;
  background: linear-gradient(90deg, #f7d184, var(--gold), #8f5f19);
  box-shadow: inset -2px 0 0 rgba(0, 0, 0, 0.18);
  transition: top 180ms ease, height 180ms ease;
  z-index: 0;
}

.pin-foot {
  position: absolute;
  left: 50%;
  bottom: 15px;
  width: 30px;
  height: 12px;
  transform: translateX(-50%);
  border-radius: 999px;
  background: linear-gradient(180deg, #f6cf83, var(--gold), #8f5f19);
  box-shadow: 0 4px 10px rgba(64, 39, 20, 0.2);
  z-index: 2;
}

.ring.is-open .ring-loop {
  --loop-top: 188px;
  border-color: var(--lacquer);
}

.ring.is-open .neighbor-link {
  opacity: 0.5;
  transform: translateY(16px) rotate(8deg);
}

.ring.is-open .ring-pin {
  top: calc(var(--loop-top) + 58px);
  height: 52px;
}

.ring.is-legal .ring-loop {
  outline: 4px solid rgba(217, 154, 43, 0.28);
  outline-offset: 4px;
}

.ring.is-hinted .ring-loop {
  outline-color: rgba(184, 50, 53, 0.56);
  box-shadow: inset 0 -5px 0 rgba(0, 0, 0, 0.12), 0 0 0 8px rgba(184, 50, 53, 0.12), 0 12px 24px rgba(184, 50, 53, 0.18);
}

.ring.is-legal:hover .ring-loop {
  transform: translateX(-50%) translateY(-6px);
}

.hint {
  margin: 0;
  padding: 12px 14px;
  border-left: 4px solid var(--jade);
  background: var(--jade-soft);
  color: #173f3a;
}

.formula-panel {
  margin-top: 18px;
  padding: 16px;
  border: 1px solid var(--line);
  background: #fffaf0;
}

.formula-panel[hidden] {
  display: none;
}

.formula-header,
.formula-grid,
.formula-row {
  display: flex;
  gap: 12px;
}

.formula-header {
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: 10px;
}

.formula-header h2 {
  font-size: 24px;
}

.formula-title-row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  padding-top: 10px;
  border-top: 1px solid rgba(139, 79, 47, 0.24);
}

.formula-title-row h3 {
  margin: 0;
  color: var(--muted);
  font-size: 14px;
}

.formula-title-row code {
  color: var(--ink);
}

.formula-symbols {
  margin: 5px 0 10px;
  color: var(--muted);
  font-size: 12px;
}

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

.formula-block {
  min-width: 0;
}

.formula-block h3 {
  margin: 0 0 8px;
  color: var(--muted);
  font-size: 14px;
}

.recurrence-block {
  margin-top: 14px;
  padding-top: 14px;
  border-top: 1px solid rgba(139, 79, 47, 0.24);
}

.inverse-block {
  margin-top: 14px;
  padding-top: 14px;
  border-top: 1px solid rgba(139, 79, 47, 0.24);
}

.recurrence-title {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 6px;
}

.recurrence-title h3 {
  margin: 0;
  color: var(--muted);
  font-size: 14px;
}

.formula-row {
  align-items: center;
  justify-content: space-between;
  padding: 6px 0;
  border-top: 1px solid rgba(139, 79, 47, 0.18);
}

.inverse-terms {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 6px 10px;
  margin: 6px 0 8px;
}

.inverse-term {
  display: grid;
  gap: 4px;
  min-width: 0;
  padding: 6px;
  border: 1px solid rgba(139, 79, 47, 0.14);
  background: rgba(255, 252, 244, 0.72);
}

.inverse-term > span {
  color: var(--muted);
  font-size: 12px;
}

.formula-row span:first-child {
  color: var(--muted);
  font-size: 13px;
}

.formula-row code,
.formula-header code,
.formula-title-row code,
.recurrence-title code {
  color: var(--ink);
}

.formula-row code,
.inverse-term code {
  align-items: center;
  flex-wrap: wrap;
  display: flex;
  gap: 3px;
  white-space: nowrap;
}

.formula-decimal {
  margin-right: 6px;
  padding: 2px 7px;
  border-radius: 3px;
  background: rgba(217, 154, 43, 0.16);
  color: var(--wood-dark);
  font-family: "Microsoft YaHei", "PingFang SC", "Segoe UI", sans-serif;
  font-size: 12px;
}

.formula-row code span,
.inverse-term code span {
  display: grid;
  place-items: center;
  width: 18px;
  height: 24px;
  border-radius: 3px;
  background: rgba(36, 117, 106, 0.08);
}

.formula-row.result code span {
  background: rgba(184, 50, 53, 0.08);
}

.formula-row code span.changed,
.formula-row.result code span.changed {
  background: #fff7f3;
  color: #d01f2f;
  border: 2px solid #d01f2f;
  box-shadow: 0 0 0 2px rgba(208, 31, 47, 0.16), 0 3px 8px rgba(143, 16, 29, 0.2);
  font-weight: 900;
}

.formula-note {
  margin: 12px 0 0;
  color: var(--muted);
  line-height: 1.6;
}

.intro {
  margin-top: 18px;
  padding-top: 16px;
  border-top: 1px solid var(--line);
}

.intro h2 {
  margin-bottom: 8px;
  font-size: 24px;
}

.intro p {
  margin: 8px 0 0;
  color: var(--muted);
  line-height: 1.7;
}

.badge {
  padding: 7px 12px;
  border-radius: 999px;
  background: var(--jade-soft);
  color: var(--jade);
  font-weight: 700;
}

.legend {
  margin: 16px 0;
  color: var(--muted);
  font-size: 13px;
}

.dot {
  display: inline-block;
  width: 10px;
  height: 10px;
  margin-right: 5px;
  border-radius: 50%;
}

.dot.mounted {
  background: var(--jade);
}

.dot.open {
  background: var(--lacquer);
}

.history-list {
  min-height: 0;
  margin: 0;
  padding: 0;
  overflow: auto;
  list-style: none;
}

.history-list li {
  padding: 12px 0;
  border-top: 1px solid var(--line);
}

.history-main,
.history-sub,
.bits {
  display: flex;
  align-items: center;
  gap: 9px;
}

.history-main {
  justify-content: space-between;
}

.history-sub {
  margin-top: 6px;
  justify-content: space-between;
  color: var(--muted);
  font-size: 12px;
}

.step {
  color: var(--muted);
  font-family: "Cascadia Mono", "Consolas", monospace;
}

.bits {
  margin-top: 8px;
}

.bits span {
  display: grid;
  place-items: center;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  color: #fffaf0;
  font-size: 12px;
  font-weight: 700;
}

.bits .one {
  background: var(--jade);
}

.bits .zero {
  background: var(--lacquer);
}

.celebration {
  position: fixed;
  inset: 0;
  z-index: 5;
  display: grid;
  place-items: center;
  padding: 24px;
  background: rgba(37, 33, 27, 0.48);
}

.celebration[aria-hidden="true"] {
  display: none;
}

.celebration-card {
  position: relative;
  width: min(460px, 100%);
  padding: 34px;
  overflow: hidden;
  background: #fffaf0;
  border: 1px solid var(--gold);
  box-shadow: 0 24px 70px rgba(0, 0, 0, 0.28);
  text-align: center;
}

.celebration-card h2 {
  font-size: 34px;
}

.celebration-card p:not(.eyebrow) {
  color: var(--muted);
}

.burst {
  position: absolute;
  inset: -45px;
  background:
    conic-gradient(from 0deg, transparent 0 10deg, rgba(217, 154, 43, 0.32) 10deg 16deg, transparent 16deg 32deg),
    radial-gradient(circle, rgba(184, 50, 53, 0.12), transparent 58%);
  animation: turn 12s linear infinite;
}

.celebration-card > *:not(.burst) {
  position: relative;
}

@keyframes turn {
  to {
    transform: rotate(1turn);
  }
}

@media (max-width: 900px) {
  .app {
    grid-template-columns: 1fr;
  }

  .history-panel {
    max-height: none;
  }
}

@media (max-width: 640px) {
  .app {
    width: min(100% - 20px, 1180px);
    padding: 10px 0;
  }

  .play-area,
  .history-panel {
    padding: 14px;
  }

  .topbar,
  .status-strip,
  .history-header {
    align-items: flex-start;
    flex-direction: column;
  }

  .controls {
    justify-content: flex-start;
  }

  .formula-header {
    flex-direction: column;
  }

  .formula-title-row,
  .recurrence-title {
    align-items: flex-start;
    flex-direction: column;
  }

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

  .inverse-terms {
    grid-template-columns: 1fr;
  }

  .formula-row {
    align-items: flex-start;
    flex-direction: column;
  }

  .formula-row code span {
    width: 16px;
    height: 22px;
  }

  .rings-stage {
    min-height: 330px;
    padding-inline: 0;
    --rings-flow-top: 38px;
    --rod-top: 66px;
    --rod-height: 16px;
    --loop-width: 48px;
    --loop-height: 57px;
    --mounted-loop-top: calc(var(--rod-top) + (var(--rod-height) / 2) - (var(--loop-height) / 2));
  }

  .spine {
    top: var(--rod-top);
  }

  .rings {
    gap: 3px;
    grid-template-columns: repeat(9, minmax(30px, 1fr));
  }

  .ring {
    height: 260px;
    --loop-top: var(--mounted-loop-top);
  }

  .ring-loop {
    width: min(48px, 96%);
    border-width: 6px;
    font-size: 12px;
  }

  .ring-label {
    width: 24px;
    height: 20px;
    font-size: 12px;
  }

  .neighbor-link {
    left: -11px;
    top: calc(var(--loop-top) + 45px);
    width: 22px;
    height: 8px;
  }

  .ring-pin {
    width: 7px;
    top: calc(var(--loop-top) + 54px);
    height: calc(230px - var(--loop-top));
  }

  .pin-foot {
    bottom: 13px;
    width: 22px;
    height: 9px;
  }

  .ring.is-open .ring-loop {
    --loop-top: 164px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation: none !important;
    transition: none !important;
  }
}