:root {
  color-scheme: light;
  --paper: #f5f4ef;
  --surface: #fbfaf6;
  --ink: #222824;
  --muted: #687069;
  --line: #cfd3cc;
  --line-strong: #9fa79f;
  --accent: #245b49;
  --accent-soft: #e2ebe5;
  --accent-strong: #173f32;
  --danger: #9b2f2f;
  --danger-soft: #f8e9e7;
  font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans JP", "Hiragino Kaku Gothic ProN", Meiryo, sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; color: var(--ink); background: var(--paper); line-height: 1.65; }
button, input, select { font: inherit; }
a { color: inherit; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 3px; }

.eyebrow,
.section-kicker {
  margin: 0 0 5px;
  color: var(--accent);
  font-size: .78rem;
  font-weight: 780;
  letter-spacing: .08em;
  text-transform: uppercase;
}

h2 { margin: 0; font-size: clamp(1.2rem, 2vw, 1.48rem); line-height: 1.35; }

.tool-shell {
  display: grid;
  grid-template-columns: minmax(0, .96fr) minmax(0, 1.04fr);
  border: 1px solid var(--line-strong);
  background: var(--surface);
}

.calculator-panel,
.visual-panel { min-width: 0; padding: 24px; }
.calculator-panel { border-right: 1px solid var(--line); }

.mode-fieldset { margin: 17px 0 21px; padding: 0; border: 0; }
.mode-fieldset legend { margin-bottom: 8px; font-weight: 760; }
.mode-options { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 6px; }
.mode-option { position: relative; display: block; cursor: pointer; }
.mode-option input { position: absolute; opacity: 0; }
.mode-option span {
  min-height: 50px;
  display: grid;
  place-items: center;
  padding: 7px 8px;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--muted);
  text-align: center;
  font-size: .86rem;
  font-weight: 700;
  line-height: 1.35;
}
.mode-option input:checked + span { border-color: var(--accent); background: var(--accent-soft); color: var(--accent); }
.mode-option input:focus-visible + span { outline: 3px solid var(--accent); outline-offset: 2px; }

.input-grid { display: grid; gap: 14px; }
.input-row label,
.output-unit-row label { display: block; margin-bottom: 5px; font-weight: 720; }
.input-wrap { display: grid; grid-template-columns: minmax(0, 1fr) minmax(104px, .38fr); align-items: stretch; gap: 6px; }
.input-wrap input,
.input-wrap select,
.output-unit-row select {
  width: 100%;
  min-width: 0;
  min-height: 44px;
  border: 1px solid var(--line-strong);
  border-radius: 2px;
  padding: 9px 10px;
  color: var(--ink);
  background: var(--surface);
}
.input-wrap input[aria-invalid="true"] { border-color: var(--danger); background: #fff8f8; }
.field-help { margin: 4px 0 0; color: var(--muted); font-size: .78rem; }
.field-error { min-height: 1.25em; margin: 2px 0 0; color: var(--danger); font-size: .82rem; }
.output-unit-row { margin-top: 14px; }
.form-error {
  margin: 12px 0 0;
  padding: 8px 10px;
  border-left: 4px solid var(--danger);
  background: var(--danger-soft);
  color: #762525;
}
.form-error[hidden] { display: none; }
.form-actions { display: flex; gap: 8px; margin-top: 17px; }
.button {
  min-height: 42px;
  border: 1px solid var(--accent);
  border-radius: 2px;
  padding: 8px 15px;
  cursor: pointer;
  font-weight: 760;
}
.button-primary { background: var(--accent); color: #fff; }
.button-primary:hover { background: var(--accent-strong); }
.button-secondary { background: var(--surface); color: var(--accent); }
.button:hover:not(:disabled) { border-color: var(--ink); }

.result-box {
  margin-top: 20px;
  padding: 15px 16px;
  border: 1px solid var(--accent);
  border-left-width: 4px;
  background: var(--accent-soft);
}
.result-box[data-state="error"] { border-color: var(--danger); background: var(--danger-soft); }
.result-label { margin: 0; color: var(--accent); font-size: .8rem; font-weight: 780; }
.result-box[data-state="error"] .result-label { color: var(--danger); }
.result-value {
  margin-top: 2px;
  font-size: clamp(1.45rem, 3.2vw, 2.05rem);
  line-height: 1.28;
  font-weight: 780;
  font-variant-numeric: tabular-nums;
  overflow-wrap: anywhere;
}
.result-status { margin: 5px 0 0; color: #3f4c46; font-size: .9rem; overflow-wrap: anywhere; }
.result-details {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin: 14px 0 0;
  border-top: 1px solid rgba(36, 91, 73, .35);
  border-left: 1px solid rgba(36, 91, 73, .35);
}
.result-details[hidden] { display: none; }
.result-details div { min-width: 0; padding: 9px 10px; border-right: 1px solid rgba(36, 91, 73, .35); border-bottom: 1px solid rgba(36, 91, 73, .35); }
.result-details .detail-wide { grid-column: 1 / -1; }
.result-details dt { color: var(--muted); font-size: .76rem; font-weight: 760; }
.result-details dd { margin: 2px 0 0; font-size: .86rem; font-weight: 650; overflow-wrap: anywhere; }

.visual-heading-row { display: flex; justify-content: space-between; align-items: flex-start; gap: 14px; }
.status-badge {
  flex: 0 0 auto;
  padding: 3px 8px;
  border: 1px solid var(--line-strong);
  background: var(--paper);
  color: var(--muted);
  font-size: .75rem;
  font-weight: 760;
}
.status-badge[data-state="ready"] { border-color: var(--accent); background: var(--accent-soft); color: var(--accent); }
.visual-metrics {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  margin: 15px 0 0;
  border-top: 1px solid var(--line);
  border-left: 1px solid var(--line);
}
.visual-metrics div { min-width: 0; padding: 9px 10px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.visual-metrics dt { color: var(--muted); font-size: .75rem; font-weight: 750; }
.visual-metrics dd { margin: 2px 0 0; font-size: .85rem; font-weight: 700; overflow-wrap: anywhere; }
.visual-stage {
  min-height: 292px;
  display: grid;
  place-items: center;
  margin-top: 15px;
  padding: 26px 16px 20px;
  overflow: hidden;
  border: 1px solid var(--line-strong);
  background: linear-gradient(180deg, #fbfaf6 0%, #f0efe9 100%);
}
.quantity-figure {
  width: 100%;
  margin: 0;
  display: grid;
  justify-items: center;
  gap: 12px;
  --container-width: 68%;
  --container-height: 132px;
  --fill-opacity: .55;
  --mass-scale: 1;
}
.container-shape {
  position: relative;
  width: var(--container-width);
  height: var(--container-height);
  max-width: 360px;
  min-width: 150px;
  min-height: 96px;
  border: 3px solid var(--accent);
  border-top-color: #4f776a;
  border-radius: 7px 7px 3px 3px;
  background: rgba(255, 255, 255, .78);
  box-shadow: inset 0 0 0 5px rgba(36, 91, 73, .06);
}
.material-fill {
  position: absolute;
  inset: 10px;
  display: grid;
  place-items: center;
  border-radius: 2px;
  background: rgba(36, 91, 73, var(--fill-opacity));
  color: #fff;
  text-shadow: 0 1px 2px rgba(0, 0, 0, .35);
  font-weight: 780;
  overflow: hidden;
}
.volume-label { position: absolute; right: 7px; bottom: 5px; padding: 1px 5px; background: rgba(251, 250, 246, .9); color: var(--accent-strong); font-size: .75rem; font-weight: 760; }
.mass-indicator {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  min-height: 34px;
  padding: 5px 10px;
  border: 1px solid var(--line-strong);
  background: var(--surface);
  color: var(--ink);
  font-size: .83rem;
  font-weight: 720;
  transform: scale(var(--mass-scale));
  transform-origin: center;
}
.mass-dot { width: 14px; height: 14px; border-radius: 50%; background: var(--accent); box-shadow: 0 0 0 4px var(--accent-soft); }
.visual-caption { margin: 0; color: var(--muted); font-size: .82rem; text-align: center; overflow-wrap: anywhere; }
.visual-description { margin: 11px 0 0; color: #38413b; font-size: .9rem; }
.scale-note { margin: 7px 0 0; padding-left: 11px; border-left: 3px solid var(--line-strong); color: var(--muted); font-size: .78rem; }

.content-section { margin-top: 30px; padding-top: 25px; border-top: 1px solid var(--line-strong); }
.section-heading { margin-bottom: 15px; }
.formula-list { display: grid; grid-template-columns: repeat(3, 1fr); border-top: 1px solid var(--line); border-left: 1px solid var(--line); }
.formula-list div { display: grid; gap: 3px; padding: 12px 13px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.formula-list span { color: var(--muted); }
.proof-guide { margin-top: 18px; border: 1px solid var(--line); }
.proof-guide h3 { margin: 0; padding: 10px 13px; border-bottom: 1px solid var(--line); color: var(--accent); font-size: .92rem; }
.proof-guide ul { display: grid; grid-template-columns: repeat(2, 1fr); margin: 0; padding: 0; list-style: none; }
.proof-guide li { padding: 10px 13px 10px 30px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); color: var(--muted); font-size: .86rem; }
.proof-guide li:nth-child(2n) { border-right: 0; }
.proof-guide li:nth-last-child(-n + 2) { border-bottom: 0; }
.proof-guide li::before { content: "—"; margin-left: -17px; margin-right: 7px; color: var(--accent); }

@media (max-width: 900px) {
  .tool-shell { grid-template-columns: 1fr; }
  .calculator-panel { border-right: 0; border-bottom: 1px solid var(--line); }
}

@media (max-width: 700px) {
  .formula-list { grid-template-columns: 1fr; }
}

@media (max-width: 600px) {
  .calculator-panel,
  .visual-panel { padding: 17px 14px; }
  .mode-options { grid-template-columns: 1fr; }
  .mode-option span { min-height: 44px; padding: 6px; font-size: .84rem; }
  .input-wrap { grid-template-columns: minmax(0, 1fr) 96px; }
  .form-actions { display: grid; grid-template-columns: 1fr; }
  .button { width: 100%; }
  .result-details { grid-template-columns: 1fr; }
  .result-details .detail-wide { grid-column: auto; }
  .visual-metrics { grid-template-columns: 1fr; }
  .visual-stage { min-height: 250px; padding-inline: 10px; }
  .container-shape { min-width: 132px; }
  .proof-guide ul { grid-template-columns: 1fr; }
  .proof-guide li,
  .proof-guide li:nth-child(2n),
  .proof-guide li:nth-last-child(-n + 2) { border-right: 0; border-bottom: 1px solid var(--line); }
  .proof-guide li:last-child { border-bottom: 0; }
}

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