:root {
  --app-ink: #222824;
  --app-muted: #687069;
  --app-line: #cfd3cc;
  --app-line-strong: #9fa79f;
  --app-accent: #245b49;
  --app-accent-soft: #e2ebe5;
  --app-blue: #33677d;
  --app-violet: #68517b;
  --app-orange: #a7642a;
  --app-danger: #9b2f2f;
  --app-surface: #fbfaf6;
  --app-paper: #f5f4ef;
}

*, *::before, *::after { box-sizing: border-box; }
button, input { font: inherit; }
a { color: inherit; }
:focus-visible { outline: 3px solid var(--app-accent); outline-offset: 3px; }
h2 { margin: 0; font-size: clamp(1.2rem, 2vw, 1.48rem); line-height: 1.35; }
p { overflow-wrap: anywhere; }

.tool-shell {
  display: grid;
  grid-template-columns: minmax(0, .92fr) minmax(0, 1.08fr);
  border: 1px solid var(--app-line-strong);
  background: var(--app-surface);
}

.calculator-panel, .visual-panel { min-width: 0; padding: 24px; }
.calculator-panel { border-right: 1px solid var(--app-line); }
.section-heading { margin-bottom: 15px; }
.eyebrow, .section-kicker {
  margin: 0 0 5px;
  color: var(--app-accent);
  font-size: .78rem;
  font-weight: 780;
  letter-spacing: .08em;
  text-transform: uppercase;
}

.input-grid { display: grid; gap: 14px; }
.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 {
  width: 100%;
  min-width: 0;
  border: 1px solid var(--app-line-strong);
  border-radius: 0;
  padding: 10px 11px;
  color: var(--app-ink);
  background: var(--app-surface);
  appearance: textfield;
}
.input-wrap input::-webkit-inner-spin-button,
.input-wrap input::-webkit-outer-spin-button { margin: 0; appearance: none; }
.input-wrap input[aria-invalid="true"] { border-color: var(--app-danger); background: #fff8f8; }
.unit {
  min-width: 60px;
  display: grid;
  place-items: center;
  padding: 0 10px;
  border: 1px solid var(--app-line-strong);
  border-left: 0;
  background: var(--app-paper);
  color: var(--app-muted);
  font-weight: 700;
}
.unit-plain { min-width: 48px; }
.field-help { min-height: 1.3em; margin: 4px 0 0; color: var(--app-muted); font-size: .78rem; }
.field-error { min-height: 1.3em; margin: 3px 0 0; color: var(--app-danger); font-size: .82rem; }
.form-error {
  margin: 13px 0 0;
  padding: 8px 10px;
  border-left: 4px solid var(--app-danger);
  background: #f8e9e7;
  color: #762525;
  font-size: .88rem;
}
.form-actions { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 17px; }
.button {
  min-height: 42px;
  border: 1px solid var(--app-accent);
  border-radius: 2px;
  padding: 8px 15px;
  cursor: pointer;
  font-weight: 760;
}
.button-primary { background: var(--app-accent); color: #fff; }
.button-primary:hover { background: #1b4738; }
.button-secondary { background: var(--app-surface); color: var(--app-accent); }
.button:hover:not(:disabled) { border-color: var(--app-ink); }
.button:disabled { border-color: var(--app-line); background: var(--app-paper); color: #8a918b; cursor: not-allowed; }

.result-box {
  margin-top: 21px;
  padding: 16px;
  border: 1px solid var(--app-accent);
  border-left-width: 4px;
  background: var(--app-accent-soft);
}
.result-box[data-state="error"] { border-color: var(--app-danger); background: #fff7f5; }
.result-heading-row { display: flex; justify-content: space-between; align-items: flex-start; gap: 12px; }
.result-label { margin: 0; color: var(--app-accent); font-size: .79rem; font-weight: 780; }
.result-box[data-state="error"] .result-label { color: var(--app-danger); }
.result-heading-row h2 { margin-top: 2px; font-size: clamp(1.03rem, 2vw, 1.28rem); }
.status-badge {
  flex: 0 0 auto;
  padding: 3px 8px;
  border: 1px solid var(--app-line-strong);
  background: var(--app-paper);
  color: var(--app-muted);
  font-size: .75rem;
  font-weight: 760;
  white-space: nowrap;
}
.status-badge[data-state="ready"], .status-badge[data-state="stable"] {
  border-color: var(--app-accent);
  background: var(--app-accent-soft);
  color: var(--app-accent);
}
.status-badge[data-state="sliding"] { border-color: var(--app-orange); background: #f7eadc; color: #7c461e; }
.status-badge[data-state="error"] { border-color: var(--app-danger); background: #f8e9e7; color: var(--app-danger); }
.metrics-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 7px;
  margin-top: 15px;
}
.metric-card {
  min-width: 0;
  display: grid;
  gap: 3px;
  padding: 9px 10px;
  border: 1px solid var(--app-line);
  background: rgba(251, 250, 246, .7);
}
.metric-card span { color: var(--app-muted); font-size: .77rem; line-height: 1.4; }
.metric-card strong { color: var(--app-ink); font-size: 1rem; line-height: 1.35; font-variant-numeric: tabular-nums; overflow-wrap: anywhere; }
.metric-card.metric-wide { grid-column: span 2; }
.metric-card.metric-wide strong { font-size: 1.08rem; }
.result-note { margin: 11px 0 0; color: #3f4c46; font-size: .86rem; }

.visual-panel { background: var(--app-paper); }
.visual-heading { display: flex; align-items: baseline; justify-content: space-between; gap: 10px; }
.diagram-figure { margin: 0; }
.diagram-figure svg {
  display: block;
  width: 100%;
  height: auto;
  min-height: 300px;
  overflow: visible;
  border: 1px solid var(--app-line-strong);
  background: var(--app-surface);
}
.diagram-ground { fill: var(--app-line-strong); }
.diagram-plane { stroke: var(--app-ink); stroke-width: 5; stroke-linecap: round; }
.diagram-height { stroke: var(--app-line); stroke-width: 1.5; stroke-dasharray: 5 5; }
.diagram-angle-arc { fill: none; stroke: var(--app-accent); stroke-width: 2; }
.diagram-block { fill: var(--app-accent-soft); stroke: var(--app-accent); stroke-width: 2; }
.diagram-block-text { fill: var(--app-accent); font-size: 18px; font-weight: 760; }
.force-vector { fill: none; stroke-width: 3; stroke-linecap: round; }
.force-gravity { stroke: var(--app-ink); }
.force-parallel { stroke: var(--app-accent); }
.force-perpendicular { stroke: var(--app-blue); }
.force-normal { stroke: var(--app-violet); }
.force-friction { stroke: var(--app-orange); }
.diagram-text { fill: var(--app-ink); font-size: 15px; font-weight: 700; paint-order: stroke; stroke: var(--app-surface); stroke-width: 4px; stroke-linejoin: round; }
.diagram-angle { fill: var(--app-accent); font-size: 16px; }
.vector-label { font-size: 13px; }
.gravity-label { fill: var(--app-ink); }
.parallel-label { fill: var(--app-accent); }
.perpendicular-label { fill: var(--app-blue); }
.normal-label { fill: var(--app-violet); }
.friction-label { fill: var(--app-orange); }
.diagram-state { fill: var(--app-muted); font-size: 13px; font-weight: 600; }
.diagram-figure figcaption { margin-top: 9px; color: var(--app-muted); font-size: .82rem; }
.legend { display: flex; flex-wrap: wrap; gap: 9px 16px; margin-top: 13px; color: var(--app-muted); font-size: .78rem; }
.legend span { display: inline-flex; align-items: center; gap: 6px; }
.legend-dot { display: inline-block; width: 9px; height: 9px; border-radius: 50%; }
.legend-gravity { background: var(--app-ink); }
.legend-component { background: var(--app-accent); }
.legend-contact { background: var(--app-violet); }

.content-section { margin-top: 30px; padding-top: 25px; border-top: 1px solid var(--app-line-strong); }
.steps-list {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0;
  margin: 0;
  padding: 0;
  border-block: 1px solid var(--app-line);
  list-style: none;
  counter-reset: steps;
}
.steps-list li {
  position: relative;
  min-width: 0;
  padding: 35px 12px 13px;
  border-right: 1px solid var(--app-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(--app-accent); font-size: .75rem; font-weight: 800; }
.formula-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); border-top: 1px solid var(--app-line); border-left: 1px solid var(--app-line); }
.formula-list div { min-width: 0; display: grid; gap: 4px; padding: 12px 13px; border-right: 1px solid var(--app-line); border-bottom: 1px solid var(--app-line); }
.formula-list div:last-child:nth-child(odd) { grid-column: span 2; }
.formula-list strong { color: var(--app-accent); font-size: 1.03rem; font-variant-numeric: tabular-nums; }
.formula-list span { color: var(--app-muted); font-size: .84rem; }
.method-note { margin: 13px 0 0; color: var(--app-muted); font-size: .88rem; }
.notes-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 0; margin: 0; padding: 0; border-top: 1px solid var(--app-line); border-left: 1px solid var(--app-line); list-style: none; }
.notes-list li { min-width: 0; padding: 11px 13px 11px 28px; border-right: 1px solid var(--app-line); border-bottom: 1px solid var(--app-line); color: var(--app-muted); font-size: .86rem; }
.notes-list li::before { content: "—"; display: inline-block; width: 18px; margin-left: -18px; color: var(--app-accent); font-weight: 800; }

@media (max-width: 900px) {
  .tool-shell { grid-template-columns: 1fr; }
  .calculator-panel { border-right: 0; border-bottom: 1px solid var(--app-line); }
}

@media (max-width: 680px) {
  .calculator-panel, .visual-panel { padding: 19px; }
  .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(--app-line); }
  .formula-list, .notes-list { grid-template-columns: 1fr; }
  .formula-list div:last-child:nth-child(odd) { grid-column: auto; }
  .notes-list li { border-right: 1px solid var(--app-line); }
  .diagram-figure svg { min-height: 250px; }
}

@media (max-width: 520px) {
  .calculator-panel, .visual-panel { padding: 16px; }
  .result-heading-row { display: grid; gap: 8px; }
  .status-badge { justify-self: start; }
  .metrics-grid { grid-template-columns: 1fr; }
  .metric-card.metric-wide { grid-column: auto; }
  .form-actions { display: grid; grid-template-columns: 1fr; }
  .form-actions .button { width: 100%; }
  .diagram-figure svg { min-height: 220px; }
  .legend { gap: 7px 12px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}