: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;
  --acid: #b66a36;
  --base: #2f7086;
  --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; }
h3 { margin: 0; font-size: 1rem; line-height: 1.4; }

.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); }
.mode-fieldset, .values-fieldset { margin: 17px 0 0; padding: 0; border: 0; }
.mode-fieldset legend, .values-fieldset legend { margin-bottom: 8px; font-weight: 760; }
.values-fieldset { margin-top: 20px; }
.mode-options { display: grid; grid-template-columns: repeat(2, 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: 48px; display: grid; place-items: center; padding: 7px 8px; border: 1px solid var(--line); background: var(--surface); color: var(--muted); text-align: center; font-size: .87rem; 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, .quantity-settings label { display: block; margin-bottom: 5px; font-weight: 720; }
.input-wrap { display: grid; grid-template-columns: minmax(0, 1fr) minmax(104px, .42fr); align-items: stretch; gap: 6px; }
.input-wrap input, .input-wrap select, .quantity-settings 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; }
.quantity-settings { display: grid; grid-template-columns: auto minmax(0, 1fr) auto minmax(0, 1fr); align-items: center; gap: 6px 9px; margin-top: 18px; }
.quantity-settings[hidden] { display: none; }
.quantity-settings .field-help { grid-column: 1 / -1; }
.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(2, 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: 316px; display: grid; place-items: center; margin-top: 15px; padding: 24px 18px 18px; overflow: hidden; border: 1px solid var(--line-strong); background: linear-gradient(180deg, #fbfaf6 0%, #edf2f2 100%); }
.buffer-figure { width: 100%; max-width: 460px; margin: 0; display: grid; gap: 16px; }
.bar-group { display: grid; grid-template-columns: 48px minmax(0, 1fr) minmax(68px, auto); align-items: center; gap: 10px; }
.bar-label { color: var(--ink); font-size: 1.1rem; font-weight: 780; text-align: center; }
.bar-track { height: 34px; overflow: hidden; border: 1px solid var(--line-strong); background: #fff; }
.bar-fill { height: 100%; width: 0; transform-origin: left center; transition: width .2s ease; }
.acid-fill { background: var(--acid); }
.base-fill { background: var(--base); }
.bar-value { min-width: 0; color: var(--muted); font-size: .82rem; font-weight: 700; overflow-wrap: anywhere; }
.ratio-mark { display: flex; justify-content: center; gap: 20px; color: var(--muted); font-size: .82rem; font-weight: 720; }
.visual-caption { margin: 0; color: var(--muted); font-size: .78rem; text-align: center; }
.visual-description, .scale-note { margin: 14px 0 0; color: var(--muted); font-size: .86rem; overflow-wrap: anywhere; }
.scale-note { margin-top: 7px; font-size: .75rem; }
.content-section { margin-top: 42px; }
.formula-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); margin-top: 16px; border-top: 1px solid var(--line); border-left: 1px solid var(--line); }
.formula-list article { min-width: 0; display: grid; gap: 4px; padding: 14px 15px; border-right: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.formula-list strong { overflow-wrap: anywhere; font-size: 1rem; }
.formula-list span { color: var(--muted); font-size: .82rem; }
.proof-guide { margin-top: 20px; padding: 17px 18px; border: 1px solid var(--line); background: var(--surface); }
.proof-guide ul { margin: 10px 0 0; padding-left: 1.25em; }
.proof-guide li + li { margin-top: 6px; }
.site-footer { margin-top: 38px; border-top: 1px solid var(--line); }
.footer-inner { display: flex; flex-wrap: wrap; align-items: center; gap: 12px 18px; padding: 20px 0 0; color: var(--muted); font-size: .8rem; }
.footer-inner a { color: var(--accent); font-weight: 700; }

@media (max-width: 760px) {
  .tool-shell { grid-template-columns: 1fr; }
  .calculator-panel { border-right: 0; border-bottom: 1px solid var(--line); }
  .quantity-settings { grid-template-columns: 1fr 1fr; }
  .quantity-settings label { margin-top: 4px; }
  .quantity-settings .field-help { grid-column: 1 / -1; }
}

@media (max-width: 460px) {
  .calculator-panel, .visual-panel { padding: 17px 14px; }
  .mode-options { grid-template-columns: 1fr; }
  .input-wrap { grid-template-columns: 1fr; }
  .quantity-settings { grid-template-columns: 1fr; }
  .quantity-settings .field-help { grid-column: 1; }
  .result-details { grid-template-columns: 1fr; }
  .result-details .detail-wide { grid-column: 1; }
  .formula-list { grid-template-columns: 1fr; }
  .bar-group { grid-template-columns: 36px minmax(0, 1fr); gap: 7px; }
  .bar-value { grid-column: 2; }
  .visual-stage { padding-inline: 10px; }
}