:root {
  color-scheme: light;
  font-family: ui-rounded, "SF Pro Rounded", "Avenir Next", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-synthesis: none;
  --ink: #172033;
  --muted: #64748b;
  --blue: #2563eb;
  --violet: #7654c4;
  --violet-deep: #5f3fac;
  --turn: #c56b20;
  --turn-soft: #f5a44f;
  --green: #087154;
}

* { box-sizing: border-box; }
html, body { min-height: 100%; }
body { margin: 0; color: var(--ink); background: radial-gradient(circle at 9% 5%, rgb(118 84 196 / 8%), transparent 28rem), #f6f7fb; overscroll-behavior: none; }
button, svg { -webkit-tap-highlight-color: transparent; }
.subtraction-shell { width: min(100%, 1480px); margin: 0 auto; padding: max(18px, env(safe-area-inset-top)) max(18px, env(safe-area-inset-right)) max(18px, env(safe-area-inset-bottom)) max(18px, env(safe-area-inset-left)); }
.subtraction-header { display: flex; align-items: flex-start; justify-content: space-between; gap: 22px; margin-bottom: 16px; }
.eyebrow { margin: 0 0 4px; color: var(--blue); font-size: clamp(.82rem, 1.5vw, 1rem); font-weight: 800; letter-spacing: .08em; text-transform: uppercase; }
h1 { max-width: 1100px; margin: 0; font-size: clamp(1.7rem, 3.8vw, 3.35rem); line-height: 1.03; letter-spacing: -.035em; }
.subtitle { margin: 6px 0 0; color: var(--muted); font-size: clamp(1rem, 1.8vw, 1.35rem); font-weight: 650; }
.local-note { flex: 0 0 auto; margin: 4px 0 0; padding: 9px 14px; border: 1px solid #b9e5d5; border-radius: 999px; color: var(--green); background: #ecfdf5; font-size: clamp(.74rem, 1.2vw, .9rem); font-weight: 750; white-space: nowrap; }
.local-note span { margin-right: 5px; font-size: .7em; }
.subtraction-visualizer, .subtraction-insight { border: 1px solid rgb(203 213 225 / 82%); border-radius: 26px; background: rgb(255 255 255 / 94%); box-shadow: 0 20px 60px rgb(30 41 59 / 9%); }
.subtraction-visualizer { min-width: 0; padding: clamp(8px, 1.4vw, 16px); }
.subtraction-stage { position: relative; min-height: 0; }
.subtraction-board { display: block; width: 100%; max-height: min(58dvh, 640px); border-radius: 20px; touch-action: none; user-select: none; }
.subtraction-prompt { position: absolute; z-index: 2; inset: 0; display: grid; place-content: center; gap: 20px; padding: 30px; text-align: center; }
.subtraction-prompt[hidden] { display: none; }
.subtraction-prompt p { margin: 0; color: var(--muted); font-size: clamp(1.2rem, 2.5vw, 1.8rem); font-weight: 760; }
.subtraction-prompt .prompt-formula { color: var(--ink); font-size: clamp(3.6rem, 10vw, 7.2rem); font-weight: 900; letter-spacing: -.05em; line-height: 1; }
.board-background { fill: #f8fafc; stroke: #dbe4ef; stroke-width: 4; }
.axis-arrow { fill: #64748b; }
.axis { stroke: #64748b; stroke-linecap: butt; stroke-width: 7; }
.tick line { stroke: rgb(37 99 235 / 58%); stroke-linecap: round; stroke-width: 5; }
.tick text { fill: var(--blue); paint-order: stroke; stroke: #f8fafc; stroke-linejoin: round; stroke-width: 11px; font-size: 34px; font-weight: 850; text-anchor: middle; }
.zero-tick line { stroke: #334155; stroke-width: 7; }
.zero-tick text { fill: #334155; }
.start-tick line { stroke-width: 8; }
.point-halo, .moving-halo, .result-halo { fill: rgb(37 99 235 / 12%); stroke: rgb(37 99 235 / 24%); stroke-width: 4; }
.point-dot, .moving-dot, .result-dot { fill: var(--blue); stroke: white; stroke-width: 7; filter: drop-shadow(0 7px 10px rgb(37 99 235 / 25%)); }
.vector-line { stroke-linecap: butt; stroke-width: 17; }
.vector-arrowhead { fill: var(--turn); }
.original-vector .vector-line { stroke: #a88be5; }
.original-arrowhead { fill: var(--violet-deep); }
.reversal-vector .vector-line { stroke: var(--turn-soft); }
.reversal-arrowhead { fill: var(--turn); }
.effective-vector .vector-line { stroke: #ed9a43; }
.effective-arrowhead { fill: var(--turn); }
.step-boundaries line { stroke-linecap: round; stroke-width: 4; }
.original-vector .step-boundaries line { stroke: var(--violet-deep); }
.reversal-vector .step-boundaries line, .effective-vector .step-boundaries line { stroke: #a55316; }
.vector-label { paint-order: stroke; stroke: #f8fafc; stroke-linejoin: round; stroke-width: 10px; font-size: 26px; font-weight: 850; text-anchor: middle; }
.original-label { fill: var(--violet-deep); }
.effective-label { fill: #9a4d12; }
.end-handle { cursor: grab; touch-action: none; }
.end-handle:active { cursor: grabbing; }
.end-handle:focus-visible { outline: none; }
.end-handle:focus-visible .handle-halo { stroke: rgb(118 84 196 / 48%); stroke-width: 7; }
.handle-halo { fill: rgb(118 84 196 / 15%); stroke: rgb(118 84 196 / 26%); stroke-width: 4; }
.handle-dot { fill: var(--violet-deep); stroke: white; stroke-width: 8; filter: drop-shadow(0 7px 10px rgb(95 63 172 / 25%)); }
.formula rect, .equations rect { fill: #fff; stroke: rgb(118 84 196 / 25%); stroke-width: 4; }
.formula text { fill: var(--ink); font-size: 45px; font-weight: 900; text-anchor: middle; }
.equations text { fill: var(--ink); font-size: 27px; font-weight: 850; text-anchor: middle; }
#subtraction-start-term.is-highlighted { fill: var(--blue); }
#subtraction-operator { fill: #9a4d12; }
#subtraction-operator.is-highlighted { paint-order: stroke; stroke: rgb(197 107 32 / 18%); stroke-width: 16px; stroke-linejoin: round; }
#subtraction-sign, #subtraction-magnitude { fill: var(--violet-deep); }
#subtraction-sign.is-highlighted, #subtraction-magnitude.is-highlighted { paint-order: stroke; stroke: rgb(118 84 196 / 18%); stroke-width: 16px; stroke-linejoin: round; }
.subtraction-insight { display: grid; grid-template-columns: minmax(0, 1fr) auto; gap: 14px 24px; margin-top: 14px; padding: clamp(16px, 2vw, 24px); align-items: center; }
.insight-text { margin: 0; font-size: clamp(1.05rem, 2vw, 1.45rem); font-weight: 820; line-height: 1.35; }
.conclusion-detail { margin: 5px 0 0; color: var(--muted); font-size: clamp(.95rem, 1.6vw, 1.15rem); font-weight: 700; }
.subtraction-controls { display: flex; gap: 10px; justify-content: flex-end; }
.primary-button, .reset-button { min-height: 56px; padding: 0 20px; border-radius: 16px; font: inherit; font-size: clamp(.95rem, 1.5vw, 1.08rem); font-weight: 850; touch-action: manipulation; }
.primary-button { border: 2px solid var(--blue); color: white; background: var(--blue); box-shadow: 0 10px 24px rgb(37 99 235 / 20%); }
.reset-button { border: 2px solid #cbd5e1; color: var(--ink); background: white; }
.primary-button:disabled, .reset-button:disabled { cursor: wait; opacity: .58; }
.primary-button:focus-visible, .reset-button:focus-visible { outline: 5px solid rgb(37 99 235 / 26%); outline-offset: 3px; }
.visually-hidden { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }
noscript { display: block; margin-top: 14px; color: #a6384d; font-weight: 700; }

@media (max-width: 760px) {
  .subtraction-shell { padding-inline: 12px; }
  .subtraction-header { display: block; }
  .local-note { display: inline-block; margin-top: 12px; }
  .subtraction-insight { grid-template-columns: 1fr; }
  .subtraction-controls { justify-content: stretch; }
  .primary-button, .reset-button { flex: 1 1 0; }
}

@media (max-width: 520px) {
  .subtraction-prompt { gap: 8px; padding: 12px; }
  .subtraction-prompt p { font-size: .95rem; line-height: 1.1; }
  .subtraction-prompt .prompt-formula { font-size: clamp(2.4rem, 13vw, 3rem); }
  .subtraction-controls { flex-direction: column; }
  .primary-button, .reset-button { width: 100%; }
}

@media (orientation: landscape) and (max-height: 820px) {
  .subtraction-shell { padding-block: 10px; }
  .subtraction-header { margin-bottom: 9px; }
  h1 { font-size: clamp(1.5rem, 3.2vw, 2.65rem); }
  .subtitle { margin-top: 3px; }
  .subtraction-board { max-height: 53dvh; }
  .subtraction-insight { margin-top: 9px; padding-block: 12px; }
}

@media (min-width: 1500px) {
  .subtraction-shell { width: min(94vw, 1660px); }
  .subtraction-board { max-height: 660px; }
}

@media (prefers-reduced-motion: reduce) {
  .point-dot, .moving-dot, .result-dot, .handle-dot { filter: none; }
}