: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;
  --plot: #5c8f9d;
  --plot-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; }

.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); }

.values-fieldset { margin: 17px 0 0; padding: 0; border: 0; }
.values-fieldset > legend { margin-bottom: 9px; font-weight: 760; }
.point-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; }
.point-card { min-width: 0; margin: 0; padding: 12px; border: 1px solid var(--line); background: #f8f7f2; }
.point-card > legend { padding: 0 5px; color: var(--accent); font-weight: 760; }
.point-inputs { display: grid; gap: 10px; }
.input-row label { display: block; margin-bottom: 5px; font-weight: 720; }
.plain-input {
  display: block;
  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);
}
.plain-input[aria-invalid="true"] { border-color: var(--danger); background: #fff8f8; }
.target-row { margin-top: 14px; padding: 12px; border: 1px solid var(--accent); background: var(--accent-soft); }
.target-row .plain-input { background: var(--surface); }
.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: .85rem; font-weight: 700; overflow-wrap: anywhere; }

.visual-stage { min-height: 318px; display: grid; place-items: center; margin-top: 15px; padding: 14px 10px 10px; overflow: hidden; border: 1px solid var(--line); background: linear-gradient(180deg, #f2f7f8 0%, #f8f4ec 100%); }
.plot-figure { position: relative; width: min(100%, 540px); margin: 0; overflow: hidden; border: 1px solid var(--line-strong); background: linear-gradient(180deg, #e7f0ef 0%, #f8f4ec 100%); }
.plot-svg { display: block; width: 100%; height: auto; min-height: 250px; }
.plot-grid-line { stroke: rgba(104,112,105,.2); stroke-width: 1; stroke-dasharray: 4 7; }
.plot-axis { stroke: #758078; stroke-width: 1.5; }
.plot-line { stroke: var(--accent); stroke-width: 3; stroke-linecap: round; }
.plot-target-guide { stroke: var(--plot); stroke-width: 1.5; stroke-dasharray: 6 5; }
.plot-point { stroke: #fff; stroke-width: 3; }
.plot-point-one,
.plot-point-two { fill: var(--accent); }
.plot-point-target { fill: var(--plot); }
.plot-label { fill: var(--accent-strong); font-size: 14px; font-weight: 750; paint-order: stroke; stroke: #f8f4ec; stroke-width: 5px; stroke-linejoin: round; }
.plot-label-target { fill: #346f7b; }
.plot-axis-label { fill: var(--ink); font-size: 14px; font-weight: 800; }
.plot-scale-label { fill: var(--muted); font-size: 11px; }
.plot-figure[data-state="waiting"] .plot-line,
.plot-figure[data-state="waiting"] .plot-target-guide,
.plot-figure[data-state="waiting"] .plot-point,
.plot-figure[data-state="waiting"] .plot-label,
.plot-figure[data-state="waiting"] .plot-scale-label { visibility: hidden; }
.visual-caption { margin: -2px 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); }
  .formula-list { grid-template-columns: repeat(3, minmax(0, 1fr)); }
}

@media (max-width: 760px) {
  .point-grid { 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) {
  .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)); }
  .plot-figure { width: 100%; }
  .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; }
}