: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;
  --load: #245b49;
  --concentration: #8b5e34;
  --flow: #4e7585;
  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; overflow-x: hidden; }
button, input { 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,
.values-fieldset { margin: 17px 0 0; padding: 0; border: 0; }
.mode-fieldset legend,
.values-fieldset legend { margin-bottom: 9px; font-weight: 760; }
.mode-options { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 6px; }
.mode-options label {
  display: flex;
  min-width: 0;
  min-height: 48px;
  align-items: center;
  gap: 7px;
  padding: 8px 9px;
  border: 1px solid var(--line-strong);
  background: var(--surface);
  cursor: pointer;
  font-size: .83rem;
  font-weight: 700;
  line-height: 1.35;
}
.mode-options label:has(input:checked) { border-color: var(--accent); background: var(--accent-soft); color: var(--accent-strong); }
.mode-options input { flex: 0 0 auto; accent-color: var(--accent); }
.mode-options span { overflow-wrap: anywhere; }
.mode-help { margin-top: 7px; }

.input-grid { display: grid; gap: 14px; }
.input-row label { display: block; margin-bottom: 5px; font-weight: 720; }
.input-wrap { display: grid; grid-template-columns: minmax(0, 1fr) minmax(98px, .38fr); align-items: stretch; gap: 6px; }
.input-wrap input,
.unit-label {
  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);
}
.unit-label { display: flex; align-items: center; color: var(--muted); font-size: .86rem; font-weight: 700; }
.input-row.is-target .input-wrap input { border-color: var(--accent); background: var(--accent-soft); color: var(--accent-strong); }
.input-row.is-target .unit-label { border-color: var(--accent); background: var(--accent-soft); color: var(--accent); }
.input-wrap input[aria-invalid="true"] { border-color: var(--danger); background: #fff8f8; }
.input-wrap input:disabled { cursor: not-allowed; opacity: .9; }
.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; }
.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 { display: block; 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(4, 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: .82rem; font-weight: 700; overflow-wrap: anywhere; }

.visual-stage { min-height: 318px; display: grid; place-items: center; margin-top: 15px; padding: 24px 12px 18px; overflow: hidden; border: 1px solid var(--line); background: linear-gradient(180deg, #f2f7f4 0%, #f8f4ec 100%); }
.relation-figure { position: relative; width: min(100%, 450px); height: 270px; margin: 0; overflow: hidden; border: 1px solid var(--line-strong); background: linear-gradient(160deg, #e6f0eb 0%, #f8f4ec 100%); }
.relation-node { position: absolute; z-index: 2; display: grid; min-width: 116px; justify-items: center; gap: 1px; padding: 9px 10px 8px; border: 2px solid currentColor; border-radius: 3px; background: rgba(251,250,246,.96); text-align: center; }
.relation-node strong { font-size: 1.35rem; line-height: 1.05; }
.relation-node span { font-size: .78rem; font-weight: 760; line-height: 1.3; }
.relation-node .node-value { font-size: .82rem; font-style: normal; font-variant-numeric: tabular-nums; line-height: 1.25; }
.relation-node small { font-size: .7rem; line-height: 1.2; }
.relation-load { left: 5%; top: 37%; color: var(--load); }
.relation-concentration { right: 5%; top: 10%; color: var(--concentration); }
.relation-flow { right: 5%; bottom: 10%; color: var(--flow); }
.relation-connector { position: absolute; z-index: 1; height: 2px; background: currentColor; color: var(--accent); transform-origin: left center; }
.relation-connector::after { content: ""; position: absolute; right: -1px; top: -5px; width: 9px; height: 9px; border-top: 2px solid currentColor; border-right: 2px solid currentColor; transform: rotate(45deg); }
.relation-connector span { position: absolute; top: -18px; left: 50%; padding: 0 5px; background: #eaf1ed; color: var(--accent); font-size: .8rem; font-weight: 800; }
.connector-load-concentration { left: 31%; top: 42%; width: 42%; transform: rotate(-22deg); }
.connector-concentration-flow { left: 78%; top: 34%; width: 24%; transform: rotate(72deg); }
.connector-load-flow { left: 31%; top: 61%; width: 49%; transform: rotate(18deg); }
.relation-figure[data-state="ready"] .relation-node { box-shadow: 0 2px 0 rgba(34,40,36,.08); }
.visual-caption { position: absolute; inset: auto 10px 7px; color: #3c5347; font-size: .73rem; line-height: 1.35; text-align: center; }
.visual-description { margin: 12px 0 0; color: var(--muted); font-size: .84rem; }
.scale-note { margin: 6px 0 0; padding-left: 11px; border-left: 3px solid var(--line-strong); color: var(--muted); font-size: .76rem; }

.content-section { margin-top: 34px; padding-top: 25px; border-top: 1px solid var(--line-strong); }
.section-heading { margin-bottom: 15px; }
.steps-list { display: grid; grid-template-columns: repeat(4, 1fr); gap: 0; margin: 0; padding: 0; border-block: 1px solid var(--line); list-style: none; counter-reset: steps; }
.steps-list li { position: relative; min-width: 0; padding: 35px 12px 13px; border-right: 1px solid var(--line); background: transparent; counter-increment: steps; font-size: .88rem; overflow-wrap: anywhere; }
.steps-list li:last-child { border-right: 0; }
.steps-list li::before { content: counter(steps, decimal-leading-zero); position: absolute; top: 7px; left: 12px; color: var(--accent); font-size: .75rem; font-weight: 800; }
.formula-list { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 8px; }
.formula-list article { display: grid; gap: 4px; min-width: 0; padding: 14px; border: 1px solid var(--line); background: var(--surface); }
.formula-list strong { overflow-wrap: anywhere; font-size: .95rem; }
.formula-list span { color: var(--muted); font-size: .82rem; }
.example-box { margin-top: 14px; padding: 14px 16px; border: 1px solid var(--accent); background: var(--accent-soft); }
.example-box h3 { margin: 0; color: var(--accent); font-size: .95rem; }
.example-box p { margin: 7px 0 0; color: #38413b; font-size: .88rem; overflow-wrap: anywhere; }
.proof-guide { margin-top: 14px; padding: 16px; border: 1px solid var(--line); background: var(--surface); }
.proof-guide h3 { margin: 0; font-size: 1rem; }
.proof-guide ul { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 0 22px; margin: 9px 0 0; padding-left: 1.2em; color: var(--muted); font-size: .84rem; }
.proof-guide li + li { margin-top: 5px; }

@media (max-width: 900px) {
  .tool-shell { grid-template-columns: 1fr; }
  .calculator-panel { border-right: 0; border-bottom: 1px solid var(--line); }
  .steps-list { grid-template-columns: repeat(2, 1fr); }
  .steps-list li:nth-child(2) { border-right: 0; }
  .steps-list li:nth-child(-n + 2) { border-bottom: 1px solid var(--line); }
  .steps-list li:nth-child(3) { border-right: 1px solid var(--line); }
}

@media (max-width: 760px) {
  .mode-options { grid-template-columns: 1fr; }
  .formula-list { grid-template-columns: 1fr; }
  .calculator-panel, .visual-panel { padding: 18px; }
  .proof-guide ul { grid-template-columns: 1fr; }
}

@media (max-width: 460px) {
  .input-wrap { grid-template-columns: minmax(0, 1fr) 96px; }
  .form-actions { flex-wrap: wrap; }
  .form-actions .button { flex: 1 1 140px; }
  .result-details { grid-template-columns: 1fr; }
  .result-details .detail-wide { grid-column: auto; }
  .visual-metrics { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .relation-figure { height: 250px; }
  .relation-node { min-width: 98px; padding-inline: 6px; }
  .relation-node span { font-size: .72rem; }
  .relation-node small { font-size: .64rem; }
  .steps-list { grid-template-columns: 1fr; }
  .steps-list li,
  .steps-list li:nth-child(2),
  .steps-list li:nth-child(3) { border-right: 0; border-bottom: 1px solid var(--line); }
  .steps-list 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; animation-iteration-count: 1 !important; }
}