:root {
  color-scheme: light;
  --paper: #f5f4ef;
  --surface: #fbfaf6;
  --ink: #222824;
  --muted: #687069;
  --line: #cfd3cc;
  --line-strong: #9fa79f;
  --accent: #245b49;
  --accent-soft: #e2ebe5;
  --water: #b8ddeb;
  --water-strong: #5278a0;
  --danger: #9b2f2f;
  --measure: 1120px;
  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; }
[hidden] { display: none !important; }
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; }

h2 { margin: 0; font-size: clamp(1.2rem, 2vw, 1.48rem); line-height: 1.35; }
.tool-shell { display: grid; grid-template-columns: minmax(0, .92fr) minmax(0, 1.08fr); 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); }
.section-heading { margin-bottom: 15px; }
.section-intro { margin: -5px 0 18px; color: var(--muted); font-size: .88rem; }
.input-grid { display: grid; gap: 13px; }
.input-row label { display: block; margin-bottom: 5px; font-weight: 700; }
.input-wrap { display: grid; grid-template-columns: minmax(0, 1fr) auto; align-items: stretch; }
.input-wrap input, .input-wrap select { min-width: 0; border: 1px solid var(--line-strong); color: var(--ink); background: var(--surface); }
.input-wrap input { width: 100%; padding: 10px 11px; }
.input-wrap select { min-width: 82px; padding: 0 26px 0 9px; border-left: 0; }
.input-wrap input[aria-invalid="true"], .input-wrap select[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: 3px 0 0; color: var(--danger); font-size: .82rem; }
.form-error { margin: 12px 0 0; padding: 8px 10px; border-left: 4px solid var(--danger); background: #f8e9e7; color: #762525; }
.form-actions { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 8px; margin-top: 17px; }
.button { min-height: 44px; 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: #1b4738; }
.button-secondary { background: var(--surface); color: var(--accent); }
.button:hover:not(:disabled) { border-color: var(--ink); }
.button:disabled { border-color: var(--line); background: var(--paper); color: #8a918b; cursor: not-allowed; }
.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: #f8e9e7; }
.result-label { margin: 0; color: var(--accent); font-size: .8rem; font-weight: 780; }
.result-box[data-state="error"] .result-label, .result-box[data-state="error"] .result-status { color: var(--danger); }
.result-value { margin-top: 2px; font-size: clamp(1.35rem, 3.1vw, 2rem); line-height: 1.28; font-weight: 780; font-variant-numeric: tabular-nums; overflow-wrap: anywhere; }
.result-status { margin: 4px 0 0; color: var(--accent); font-weight: 750; }
.result-formula { 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: 15px 0 0; border-top: 1px solid var(--line); border-left: 1px solid var(--line); }
.result-details[hidden], .visual-details[hidden] { display: none; }
.result-details div { min-width: 0; padding: 8px 10px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.result-details dt { color: var(--muted); font-size: .75rem; font-weight: 750; }
.result-details dd { margin: 2px 0 0; font-size: .87rem; font-weight: 700; 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); }
.status-badge[data-state="error"] { border-color: var(--danger); background: #f8e9e7; color: var(--danger); }
.diagram-frame { margin: 15px 0 0; }
.diagram-frame svg { display: block; width: 100%; height: auto; border: 1px solid var(--line-strong); background: #eef3f0; }
.diagram-frame figcaption { margin-top: 9px; color: #38413b; font-size: .86rem; }
.tank-outline { fill: none; stroke: #697b78; stroke-width: 3; }
.water-fill { fill: var(--water); opacity: .82; }
.water-surface { stroke: var(--water-strong); stroke-width: 4; }
.tank-base { stroke: #697b78; stroke-width: 5; stroke-linecap: round; }
.object-block { fill: url(#object-hatch); stroke: #8b6d39; stroke-width: 2; }
.object-submerged { fill: #85bed5; opacity: .82; }
.depth-line { stroke: var(--water-strong); stroke-width: 2.5; stroke-dasharray: 6 5; }
.pressure-arrow { stroke: var(--water-strong); stroke-width: 3; }
.force-arrow { stroke-width: 5; stroke-linecap: round; }
.force-up { stroke: var(--accent); }
.force-down { stroke: var(--danger); }
.diagram-label { fill: var(--ink); font-size: 15px; font-weight: 700; }
.surface-label { fill: var(--water-strong); font-size: 14px; }
.depth-label, .pressure-label { fill: var(--water-strong); }
.force-label { font-size: 14px; }
.force-up-label { fill: var(--accent); }
.force-down-label { fill: var(--danger); }
.diagram-placeholder { fill: var(--muted); font-size: 14px; font-weight: 650; }
.visual-legend { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 7px; margin-top: 12px; color: var(--muted); font-size: .76rem; }
.visual-legend span { display: flex; align-items: center; gap: 6px; min-width: 0; }
.legend-swatch { display: inline-block; flex: 0 0 21px; height: 4px; border-radius: 2px; }
.legend-up { background: var(--accent); }
.legend-down { background: var(--danger); }
.legend-pressure { background: var(--water-strong); }
.visual-description { min-height: 3.2em; margin: 12px 0 0; color: #38413b; font-size: .9rem; }
.visual-details { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); margin-top: 10px; border-top: 1px solid var(--line); border-left: 1px solid var(--line); }
.visual-details section { min-width: 0; padding: 9px 10px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.visual-details h3 { margin: 0; color: var(--muted); font-size: .75rem; }
.visual-details p { margin: 3px 0 0; font-size: .81rem; font-weight: 650; overflow-wrap: anywhere; }

.content-section { margin-top: 30px; padding-top: 25px; border-top: 1px solid var(--line-strong); }
.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); 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(5, minmax(0, 1fr)); border-top: 1px solid var(--line); border-left: 1px solid var(--line); }
.formula-list div { display: grid; gap: 3px; min-width: 0; padding: 12px 13px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.formula-list strong { white-space: nowrap; }
.formula-list span { color: var(--muted); font-size: .84rem; }
.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 { min-width: 0; 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); }
  .steps-list { grid-template-columns: repeat(2, 1fr); }
  .steps-list li { border-bottom: 1px solid var(--line); }
  .formula-list { grid-template-columns: repeat(3, minmax(0, 1fr)); }
}
@media (max-width: 700px) {
  .formula-list { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .visual-legend { grid-template-columns: 1fr; }
}
@media (max-width: 600px) {
  .calculator-panel, .visual-panel { padding: 17px 14px; }
  .form-actions { grid-template-columns: 1fr; }
  .button { width: 100%; }
  .result-details, .visual-details, .proof-guide ul { grid-template-columns: 1fr; }
  .result-details div, .visual-details section { border-right: 0; }
  .formula-list { grid-template-columns: 1fr; }
  .formula-list strong { white-space: normal; }
  .steps-list { grid-template-columns: 1fr; }
  .steps-list li { border-right: 0; }
  .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; }
  .visual-heading-row { gap: 8px; }
  .status-badge { max-width: 42%; text-align: center; }
}
@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; }
}