: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;
  --ion-a: #2f7086;
  --ion-b: #9b5c2f;
  --solid: #76538e;
  --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; }
h2 { margin: 0; font-size: clamp(1.2rem, 2vw, 1.48rem); line-height: 1.35; }
h3 { margin: 0; font-size: 1rem; }
.eyebrow, .section-kicker { margin: 0 0 5px; color: var(--accent); font-size: .78rem; font-weight: 780; letter-spacing: .08em; text-transform: uppercase; }

.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: 13px; }
.input-row label { display: block; margin-bottom: 5px; font-weight: 720; }
.input-wrap { display: grid; grid-template-columns: minmax(0, 1fr) minmax(120px, .53fr); align-items: stretch; gap: 6px; }
.input-wrap input, .input-wrap 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"], .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: 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(1.35rem, 3vw, 1.95rem); 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: .84rem; font-weight: 700; overflow-wrap: anywhere; }
.visual-stage { min-height: 316px; display: grid; place-items: center; margin-top: 15px; padding: 22px 12px 18px; overflow: hidden; border: 1px solid var(--line-strong); background: linear-gradient(180deg, #fbfaf6 0%, #edf2f2 100%); }
.solution-figure { width: 100%; max-width: 450px; margin: 0; display: grid; gap: 12px; justify-items: center; --solid-opacity: 0; --ion-scale: 1; }
.beaker { position: relative; width: min(82%, 260px); height: 172px; border: 4px solid #49656c; border-top: 0; border-radius: 0 0 30px 30px; background: linear-gradient(to top, rgba(83, 164, 188, .34), rgba(83, 164, 188, .08)); overflow: hidden; }
.solution-liquid { position: absolute; inset: 38% 0 0; background: rgba(83, 164, 188, .22); border-top: 2px solid #5794a2; }
.ion { position: absolute; z-index: 2; display: grid; place-items: center; width: 30px; height: 30px; border-radius: 50%; color: #fff; font-size: .82rem; font-weight: 800; transform: scale(var(--ion-scale)); }
.ion-a { background: var(--ion-a); }
.ion-b { background: var(--ion-b); }
.ion-a1 { left: 26%; top: 52%; }.ion-a2 { left: 62%; top: 70%; }.ion-b1 { left: 46%; top: 45%; }.ion-b2 { left: 70%; top: 31%; }
.precipitate { position: absolute; z-index: 3; left: 50%; bottom: 8px; transform: translateX(-50%); min-width: 74px; padding: 5px 10px; border-radius: 12px; background: var(--solid); color: #fff; text-align: center; font-size: .8rem; font-weight: 760; opacity: var(--solid-opacity); }
.diagram-labels { display: flex; flex-wrap: wrap; justify-content: center; gap: 7px; }
.diagram-labels span { min-width: 70px; padding: 4px 8px; border: 1px solid var(--line); background: var(--surface); color: var(--muted); text-align: center; font-size: .78rem; font-weight: 740; }
.diagram-labels span:last-child { min-width: 100px; color: var(--accent); }
.visual-caption { margin: 0; color: var(--muted); text-align: center; font-size: .82rem; }
.visual-description, .scale-note { margin: 11px 0 0; font-size: .86rem; }
.visual-description { color: #3f4c46; }.scale-note { color: var(--muted); font-size: .76rem; }

.content-section { margin-top: 34px; }
.formula-list { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 8px; margin-top: 15px; }
.formula-list article { min-width: 0; display: grid; gap: 3px; padding: 13px; border: 1px solid var(--line); background: var(--surface); }
.formula-list strong { font-size: 1rem; overflow-wrap: anywhere; }.formula-list span { color: var(--muted); font-size: .82rem; }
.proof-guide { margin-top: 12px; padding: 15px 17px; border-left: 4px solid var(--accent); background: var(--surface); }
.proof-guide ul { margin: 8px 0 0; padding-left: 1.25rem; }.proof-guide li { margin: 4px 0; }

@media (max-width: 940px) {
  .tool-shell { grid-template-columns: 1fr; }
  .calculator-panel { border-right: 0; border-bottom: 1px solid var(--line); }
}
@media (max-width: 600px) {
  .calculator-panel, .visual-panel { padding: 17px 14px; }
  .mode-options, .formula-list { grid-template-columns: 1fr 1fr; }
  .input-wrap { grid-template-columns: minmax(0, 1fr) minmax(100px, .56fr); }
  .result-details { grid-template-columns: 1fr; }.result-details .detail-wide { grid-column: auto; }
  .visual-stage { min-height: 286px; padding-left: 6px; padding-right: 6px; }
  .beaker { width: min(88%, 240px); }
  .formula-list { gap: 6px; }.formula-list article { padding: 10px; }
}
@media (max-width: 380px) {
  .mode-options { grid-template-columns: 1fr; }
  .input-wrap { grid-template-columns: minmax(0, 1fr) minmax(94px, .58fr); }
  .form-actions .button { flex: 1 1 100%; }
}