: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;
  --pipe: #788894;
  --pipe-dark: #52626d;
  --fluid: #5c8f9d;
  --fluid-soft: #dcebed;
  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; }

.intro .assumption {
  max-width: 730px;
  margin: 9px 0 0;
  padding-left: 11px;
  border-left: 3px solid var(--line-strong);
  color: var(--muted);
  font-size: .82rem;
}

.tool-shell {
  display: grid;
  grid-template-columns: minmax(0, .98fr) minmax(0, 1.02fr);
  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); }

.values-fieldset { margin: 17px 0 0; padding: 0; border: 0; }
.values-fieldset legend { margin-bottom: 9px; font-weight: 760; }
.input-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }
.input-row { min-width: 0; }
.input-row-wide { grid-column: 1 / -1; }
.input-row label { display: block; margin-bottom: 5px; font-weight: 720; }
.input-wrap { display: grid; grid-template-columns: minmax(0, 1fr) auto; align-items: stretch; gap: 6px; }
.input-wrap input {
  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; }
.input-unit {
  display: grid;
  min-width: 66px;
  place-items: center;
  padding: 0 9px;
  border: 1px solid var(--line-strong);
  background: var(--paper);
  color: var(--muted);
  font-size: .8rem;
  white-space: nowrap;
}
.field-help { margin: 4px 0 0; color: var(--muted); font-size: .78rem; overflow-wrap: anywhere; }
.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; flex-wrap: wrap; 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(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: 318px;
  display: grid;
  place-items: center;
  margin-top: 15px;
  padding: 24px 12px 18px;
  overflow: hidden;
  border: 1px solid var(--line);
  background: linear-gradient(180deg, #f2f7f8 0%, #f8f4ec 100%);
}
.pipe-figure {
  position: relative;
  width: min(100%, 460px);
  height: 270px;
  margin: 0;
  overflow: hidden;
  border: 1px solid var(--line-strong);
  background: linear-gradient(180deg, #e7f0ef 0%, #f8f4ec 100%);
}
.pipe-figure[data-state="ready"] { --pipe-highlight: #68818b; }
.pipe-wall {
  position: absolute;
  top: 82px;
  right: 9%;
  left: 9%;
  height: 104px;
  border: 15px solid var(--pipe-dark);
  border-radius: 56px;
  background: var(--pipe);
  box-shadow: inset 0 0 0 2px rgba(255,255,255,.25);
}
.pipe-fluid {
  position: absolute;
  top: 97px;
  right: 12%;
  left: 12%;
  height: 74px;
  display: grid;
  place-items: center;
  border-radius: 40px;
  background: linear-gradient(180deg, rgba(92,143,157,.9), rgba(92,143,157,.55));
  color: #fff;
  text-shadow: 0 1px 2px rgba(0,0,0,.38);
  font-size: .8rem;
  font-weight: 760;
}
.flow-arrow {
  position: absolute;
  top: 48px;
  right: 28%;
  left: 28%;
  color: var(--fluid);
  text-align: center;
  font-size: .95rem;
  font-weight: 800;
}
.flow-arrow::before { content: ""; position: absolute; top: 50%; right: 0; left: 0; border-top: 2px solid var(--fluid); }
.flow-arrow span { position: relative; z-index: 1; padding: 0 8px; background: #e7f0ef; }
.pressure-marker {
  position: absolute;
  top: 122px;
  padding: 3px 7px;
  border: 1px solid var(--accent);
  background: rgba(251,250,246,.94);
  color: var(--accent);
  font-size: .78rem;
  font-weight: 780;
}
.pressure-in { left: 3%; }
.pressure-out { right: 3%; color: var(--muted); border-color: var(--line-strong); }
.pipe-dimension { position: absolute; color: var(--accent); font-size: .78rem; font-weight: 780; }
.pipe-diameter { top: 82px; right: 5%; bottom: 88px; border-right: 2px solid var(--accent); }
.pipe-diameter::before,
.pipe-diameter::after { content: ""; position: absolute; right: -6px; width: 9px; height: 9px; border-right: 2px solid var(--accent); }
.pipe-diameter::before { top: -1px; border-top: 2px solid var(--accent); transform: rotate(-45deg); }
.pipe-diameter::after { bottom: -1px; border-bottom: 2px solid var(--accent); transform: rotate(-45deg); }
.pipe-diameter span { position: absolute; top: 42%; right: 6px; padding: 0 3px; background: #e7f0ef; }
.pipe-length { right: 19%; bottom: 53px; left: 19%; border-top: 2px solid var(--accent); text-align: center; }
.pipe-length::before,
.pipe-length::after { content: ""; position: absolute; top: -6px; width: 9px; height: 9px; border-top: 2px solid var(--accent); }
.pipe-length::before { left: 0; border-left: 2px solid var(--accent); transform: rotate(-45deg); }
.pipe-length::after { right: 0; border-right: 2px solid var(--accent); transform: rotate(45deg); }
.pipe-length span { position: relative; top: 5px; padding: 0 6px; background: #f8f4ec; }
.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; overflow-wrap: anywhere; }
.scale-note { margin: 6px 0 0; padding-left: 11px; border-left: 3px solid var(--line-strong); color: var(--muted); font-size: .76rem; overflow-wrap: anywhere; }

.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) {
  .calculator-panel, .visual-panel { padding: 18px; }
  .formula-list { grid-template-columns: 1fr; }
  .proof-guide ul { grid-template-columns: 1fr; }
}

@media (max-width: 560px) {
  .input-grid { grid-template-columns: 1fr; }
  .input-row-wide { grid-column: auto; }
  .result-details { grid-template-columns: 1fr; }
  .result-details .detail-wide { grid-column: auto; }
}

@media (max-width: 460px) {
  .input-wrap { grid-template-columns: minmax(0, 1fr) auto; }
  .form-actions .button { flex: 1 1 140px; }
  .visual-metrics { grid-template-columns: 1fr; }
  .pipe-figure { height: 250px; }
  .pipe-wall { top: 73px; height: 96px; }
  .pipe-fluid { top: 87px; height: 68px; }
  .flow-arrow { top: 42px; }
  .pressure-marker { top: 111px; }
  .pipe-diameter { top: 73px; bottom: 81px; }
  .pipe-length { bottom: 48px; }
  .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; }
}