:root {
  --paper: #fffdf7;
  --surface: #ffffff;
  --ink: #26344c;
  --muted: #69768a;
  --line: #e6dfd3;
  --orange: #e9843b;
  --orange-dark: #b8511f;
  --gold: #f3c558;
  --teal: #2b988b;
  --teal-soft: #e4f5f1;
  --blue: #5574ca;
  --shadow: 0 22px 60px rgba(92, 66, 34, .13);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  min-width: 320px;
  margin: 0;
  overflow-x: hidden;
  color: var(--ink);
  font-family: "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  background:
    radial-gradient(circle at 8% 4%, rgba(243, 197, 88, .2), transparent 24rem),
    radial-gradient(circle at 92% 16%, rgba(43, 152, 139, .12), transparent 28rem),
    linear-gradient(180deg, #fffdf9 0%, #f7f3eb 100%);
  line-height: 1.55;
}

button { font: inherit; cursor: pointer; }
h1, h2, p { margin-top: 0; }

.site-topbar {
  border-bottom-color: rgba(125, 99, 68, .13);
  color: var(--ink);
  background: rgba(255, 253, 247, .9);
}
.site-brand { color: var(--ink); }
.site-mark {
  border-color: rgba(233, 132, 59, .3);
  color: #713512;
  background: linear-gradient(145deg, #ffe49b, #f7b85e);
  box-shadow: 0 8px 20px rgba(199, 112, 35, .16);
}
.site-links a { color: #667184; }
.site-links a:hover,
.site-links a.active {
  border-color: #e5d7c5;
  color: #7a3b17;
  background: #fff3df;
}

.equivalence-page {
  width: min(1180px, calc(100% - 40px));
  margin: 0 auto;
}

.tool-heading { padding: 28px 0 17px; text-align: center; }
.eyebrow {
  margin-bottom: 6px;
  color: var(--orange-dark);
  font-size: 12px;
  font-weight: 900;
  letter-spacing: .04em;
}
.tool-heading h1 {
  margin-bottom: 8px;
  color: #253149;
  font-size: clamp(31px, 4.1vw, 48px);
  line-height: 1.12;
  letter-spacing: -.025em;
}
.lead {
  max-width: 790px;
  margin: 0 auto;
  color: var(--muted);
  font-size: 15px;
  font-weight: 650;
}
.chips {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 7px;
  margin-top: 11px;
}
.chip {
  min-height: 28px;
  display: inline-flex;
  align-items: center;
  padding: 4px 9px;
  border: 1px solid #e7ddce;
  border-radius: 999px;
  color: #625747;
  background: rgba(255, 255, 255, .72);
  font-size: 11px;
  font-weight: 850;
}

.equivalence-lab {
  overflow: hidden;
  border: 1px solid rgba(185, 150, 105, .25);
  border-radius: 28px;
  background: rgba(255, 255, 255, .94);
  box-shadow: var(--shadow);
}
.lab-toolbar {
  min-height: 58px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 13px 18px;
  border-bottom: 1px solid #eadfce;
  background: linear-gradient(90deg, #fffaf0, #f8fffd);
}
.lab-title { display: inline-flex; align-items: center; gap: 9px; white-space: nowrap; }
.lab-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--teal);
  box-shadow: 0 0 0 5px rgba(43, 152, 139, .12);
}
.phase-copy {
  margin: 0;
  color: var(--muted);
  font-size: 13px;
  font-weight: 750;
  text-align: right;
}

.lab-grid { display: grid; grid-template-columns: minmax(0, 1fr) minmax(290px, 340px); }
.visual-stage {
  min-width: 0;
  padding: 18px;
  border-right: 1px solid #eadfce;
  background:
    radial-gradient(circle at 24% 50%, rgba(243, 197, 88, .16), transparent 18rem),
    radial-gradient(circle at 88% 78%, rgba(43, 152, 139, .09), transparent 18rem),
    #fffaf1;
}
.equation-band {
  min-height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  padding: 9px 15px;
  border: 1px solid #eadcc8;
  border-radius: 15px;
  color: #6c6052;
  background: rgba(255, 255, 255, .84);
}
.equation-band span { font-size: 12px; font-weight: 850; }
.equation-band strong {
  color: #253149;
  font-size: clamp(25px, 3vw, 34px);
  line-height: 1;
  white-space: nowrap;
}

.circle-scene {
  min-height: 322px;
  display: grid;
  grid-template-columns: minmax(250px, 1fr) minmax(170px, .55fr);
  place-items: center;
  gap: 28px;
  padding: 15px 26px;
}
.circle-holder {
  width: min(270px, 64vw);
  aspect-ratio: 1;
  display: grid;
  place-items: center;
  border: 1px dashed rgba(185, 127, 61, .45);
  border-radius: 50%;
  background: rgba(255, 255, 255, .35);
  filter: drop-shadow(0 15px 17px rgba(123, 71, 24, .14));
}
.equivalence-circle-svg {
  width: 92%;
  height: auto;
  display: block;
  overflow: visible;
  border-radius: 50%;
}
.equivalence-sector {
  fill: var(--sector-color);
  stroke: rgba(108, 63, 29, .48);
  stroke-width: 1.25;
  transition: fill .32s ease, stroke .32s ease;
}
.equivalence-ring {
  fill: none;
  stroke: rgba(105, 58, 20, .58);
  stroke-width: 2.5;
}
.equivalence-ornament {
  fill: none;
  stroke: rgba(255, 248, 219, .85);
  stroke-width: 1.7;
  stroke-dasharray: 3 4;
}
[data-tool-state="refining"] .circle-holder { animation: hold-steady .36s ease; }
[data-tool-state="settled"] .equivalence-circle-svg { animation: refine-arrive .36s ease both; }

.fraction-reading {
  display: grid;
  place-items: center;
  gap: 8px;
  color: #74685a;
  text-align: center;
  font-size: 12px;
  font-weight: 850;
}
.fraction-reading > strong {
  min-width: 84px;
  display: grid;
  place-items: center;
  color: var(--orange-dark);
  font-size: 38px;
  line-height: .95;
}
.fraction-reading > strong i {
  width: 68px;
  height: 3px;
  margin: 6px 0;
  border-radius: 999px;
  background: #344158;
}

.invariant-line {
  min-height: 58px;
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  align-items: center;
  gap: 9px;
  padding: 9px 13px;
  border: 1px solid rgba(43, 152, 139, .32);
  border-radius: 15px;
  color: #627168;
  background: var(--teal-soft);
  font-size: 11px;
  font-weight: 800;
}
.invariant-line span { text-align: center; }
.invariant-line strong { display: block; color: #226d65; font-size: 13px; }

.control-deck { min-width: 0; padding: 20px; background: #fff; }
.control-heading span { color: var(--teal); font-size: 11px; font-weight: 900; }
.control-heading h2 { margin: 3px 0 13px; font-size: 23px; line-height: 1.2; }
.preset-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 7px; }
.case-button {
  min-width: 0;
  min-height: 58px;
  display: grid;
  place-items: center;
  gap: 2px;
  padding: 8px 5px;
  border: 1px solid #e1d7c9;
  border-radius: 12px;
  color: #4b5568;
  background: #fffaf2;
}
.case-button strong { font-size: 17px; }
.case-button span { color: #918679; font-size: 9px; font-weight: 800; white-space: nowrap; }
.case-button:hover,
.case-button:focus-visible { border-color: var(--orange); background: #fff5e6; }
.case-button[aria-checked="true"] {
  border-color: #da7732;
  color: #713513;
  background: linear-gradient(145deg, #fff0ce, #ffe4bd);
  box-shadow: inset 0 0 0 1px rgba(218, 119, 50, .14);
}
.case-button:disabled { cursor: wait; opacity: .7; }

.action-row { display: grid; grid-template-columns: minmax(0, 1fr) 76px; gap: 8px; margin-top: 12px; }
.primary-action,
.reset-button { min-height: 48px; border-radius: 12px; font-weight: 900; }
.primary-action {
  border: 1px solid var(--orange-dark);
  color: #fff;
  background: linear-gradient(135deg, #e8742a, #c95822);
  box-shadow: 0 12px 24px rgba(199, 88, 34, .2);
}
.primary-action:hover:not(:disabled) { transform: translateY(-1px); }
.primary-action:disabled { cursor: default; opacity: .62; box-shadow: none; }
.reset-button { border: 1px solid #d9cfc0; color: #5d6573; background: #fff; }
.reset-button:hover { border-color: var(--teal); color: #246d65; }

.fraction-trail {
  min-height: 51px;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 20px;
  margin-top: 14px;
  padding: 8px 10px;
  border-radius: 12px;
  background: #f7f6f2;
}
.fraction-trail span {
  position: relative;
  color: #9b948a;
  font-size: 15px;
  font-weight: 900;
}
.fraction-trail span[data-has-next="true"]::after {
  position: absolute;
  left: calc(100% + 7px);
  color: #b8afa3;
  content: "→";
}
.fraction-trail .is-done { color: #5d7f79; }
.fraction-trail .is-current { color: var(--orange-dark); font-size: 19px; }

.transform-copy {
  min-height: 41px;
  margin: 12px 0 0;
  color: #677385;
  font-size: 11px;
  font-weight: 800;
  text-align: center;
}
.truth-note {
  margin: 12px 0 0;
  padding: 10px 11px;
  border-left: 3px solid var(--gold);
  border-radius: 9px;
  color: #685328;
  background: #fff8e5;
  font-size: 11px;
  font-weight: 850;
}
:where(.case-button, .primary-action, .reset-button):focus-visible {
  outline: 3px solid rgba(85, 116, 202, .3);
  outline-offset: 3px;
}
.resource-strip {
  border-color: rgba(185, 150, 105, .26);
  border-radius: 18px;
  box-shadow: 0 14px 36px rgba(92, 66, 34, .09);
}
.trial-pill { color: #6c3214; background: #ffe7bd; }
.strip-button.primary { border-color: var(--teal); background: var(--teal); }

@keyframes hold-steady {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.025); }
}
@keyframes refine-arrive {
  from { opacity: .45; transform: rotate(-2deg) scale(.97); }
  to { opacity: 1; transform: rotate(0) scale(1); }
}

@media (max-width: 980px) {
  .lab-grid { grid-template-columns: 1fr; }
  .visual-stage { border-right: 0; border-bottom: 1px solid #eadfce; }
  .circle-scene { min-height: 300px; }
  .control-deck { display: grid; grid-template-columns: 150px minmax(0, 1fr); gap: 10px 18px; }
  .control-heading { grid-row: span 2; }
  .action-row { margin-top: 0; }
  .fraction-trail { margin-top: 0; }
  .transform-copy,
  .truth-note { grid-column: 1 / -1; margin-top: 0; }
}

@media (max-width: 720px) {
  .equivalence-page { width: calc(100% - 28px); }
  .tool-heading { padding: 21px 0 14px; }
  .tool-heading h1 { font-size: clamp(28px, 8vw, 39px); }
  .lead { font-size: 14px; }
  .lab-toolbar { align-items: flex-start; flex-direction: column; gap: 3px; }
  .phase-copy { text-align: left; }
  .circle-scene { grid-template-columns: 1fr auto; gap: 12px; padding: 14px 8px; }
  .circle-holder { width: min(240px, 60vw); }
  .control-deck { display: block; }
  .action-row,
  .fraction-trail,
  .transform-copy,
  .truth-note { margin-top: 12px; }
}

@media (max-width: 430px) {
  .site-nav { gap: 6px; }
  .site-links a { font-size: 12px; }
  .tool-heading { padding-top: 16px; }
  .tool-heading h1 { margin-bottom: 6px; font-size: 27px; }
  .lead { font-size: 13px; }
  .chips { margin-top: 8px; }
  .chip { min-height: 25px; font-size: 10px; }
  .equivalence-lab { border-radius: 20px; }
  .lab-toolbar { min-height: 52px; padding: 10px 12px; }
  .lab-title { font-size: 13px; white-space: normal; }
  .phase-copy { font-size: 11px; }
  .visual-stage { padding: 11px; }
  .equation-band { min-height: 50px; padding: 8px 10px; }
  .equation-band strong { font-size: 23px; }
  .circle-scene { min-height: 230px; }
  .circle-holder { width: min(205px, 58vw); }
  .fraction-reading { gap: 4px; font-size: 10px; }
  .fraction-reading > strong { min-width: 62px; font-size: 30px; }
  .fraction-reading > strong i { width: 50px; margin: 4px 0; }
  .invariant-line { grid-template-columns: 1fr; gap: 5px; padding: 8px 10px; }
  .invariant-line span { display: flex; justify-content: space-between; gap: 8px; }
  .invariant-line strong { display: inline; font-size: 11px; }
  .control-deck { padding: 14px; }
  .control-heading { display: flex; align-items: baseline; justify-content: space-between; gap: 8px; }
  .control-heading h2 { margin-bottom: 10px; font-size: 19px; }
  .control-heading span { font-size: 9px; }
  .case-button { min-height: 50px; }
  .fraction-trail { min-height: 44px; }
  .truth-note { padding: 8px 9px; font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    scroll-behavior: auto !important;
    animation-duration: .01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .01ms !important;
  }
}