/* ═══════════════════════════════════════════════════════════════
   AREA CALCULATOR — colourful, school-friendly area simulator
   Accent: #ff6fb1 (pink-coral)
   ═══════════════════════════════════════════════════════════════ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #0d1117;
  --surface: #161b27;
  --surface2: #1f2535;
  --border: #2a3050;
  --accent: #ff6fb1;
  --accent-lo: rgba(255, 111, 177, 0.22);
  --accent-2: #4cc9f0;
  --accent-3: #ffd166;
  --accent-4: #95e06c;
  --green: #3ddc84;
  --red: #ff5555;
  --gold: #f5c842;
  --text: #dde3f0;
  --text-dim: #6b7a99;
  --font: 'Segoe UI', system-ui, sans-serif;
  --mono: 'Courier New', monospace;
  --radius: 12px;
}

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.55;
}

#app {
  max-width: 1280px;
  margin: 0 auto;
  padding: 24px 24px 80px;
}

/* ── Header ── */
header { margin-bottom: 18px; }
header h1 {
  font-size: clamp(1.6rem, 3.5vw, 2.3rem);
  font-weight: 800;
  background: linear-gradient(135deg, var(--accent), var(--accent-3) 50%, var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  margin-bottom: 4px;
  letter-spacing: -0.5px;
}
header .subtitle { color: var(--text-dim); font-size: 0.95rem; }

/* ── Controls bar ── */
.controls-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 14px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 12px 16px;
  margin-bottom: 14px;
}
.ctrl-group { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.ctrl-label {
  font-size: 0.78rem; font-weight: 700; color: var(--text-dim);
  text-transform: uppercase; letter-spacing: 0.5px;
}

/* ── Pill tabs ── */
.pill-tabs { display: flex; gap: 4px; background: var(--bg); padding: 4px; border-radius: 8px; border: 1px solid var(--border); flex-wrap: wrap; }
.pill {
  border: none; background: transparent; color: var(--text-dim);
  padding: 6px 14px; font-size: 0.85rem; font-weight: 700;
  border-radius: 6px; cursor: pointer; transition: all .15s;
  font-family: inherit;
}
.pill:hover { color: var(--text); background: var(--surface2); }
.pill.active {
  background: linear-gradient(135deg, var(--accent), var(--accent-3));
  color: #1a0a14;
  box-shadow: 0 0 12px var(--accent-lo);
}

/* ── Buttons ── */
.btn {
  border: 1px solid var(--border); background: var(--surface2); color: var(--text);
  padding: 8px 16px; font-size: 0.85rem; font-weight: 700;
  border-radius: 8px; cursor: pointer; font-family: inherit;
  transition: all .15s; min-height: 36px;
}
.btn:hover { background: var(--accent-lo); border-color: var(--accent); color: var(--accent); }
.btn-primary {
  background: linear-gradient(135deg, var(--accent), #d44d8d);
  border-color: transparent; color: #fff;
  box-shadow: 0 4px 14px rgba(255, 111, 177, 0.35);
}
.btn-primary:hover { transform: translateY(-1px); box-shadow: 0 6px 20px rgba(255, 111, 177, 0.5); color: #fff; }
.btn-ghost { background: transparent; }
.btn-guide {
  margin-left: auto;
  background: var(--surface2); border: 1px solid var(--border); color: var(--text);
  padding: 8px 14px; border-radius: 8px; font-size: 0.82rem; font-weight: 600;
  text-decoration: none; display: inline-flex; align-items: center; gap: 6px;
}
.btn-guide:hover { border-color: var(--accent); color: var(--accent); }

/* ── Shape chips ── */
.shape-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(108px, 1fr));
  gap: 8px;
  width: 100%;
  margin-top: 6px;
}
.shape-chip {
  background: var(--bg);
  border: 1.5px solid var(--border);
  border-radius: 10px;
  padding: 10px 6px 8px;
  display: flex; flex-direction: column; align-items: center; gap: 6px;
  cursor: pointer;
  transition: all .18s;
  font-family: inherit;
  color: var(--text);
}
.shape-chip:hover { border-color: var(--accent); transform: translateY(-2px); box-shadow: 0 4px 14px var(--accent-lo); }
.shape-chip.active {
  border-color: var(--accent);
  background: linear-gradient(180deg, var(--accent-lo), transparent);
  box-shadow: 0 0 14px var(--accent-lo);
}
.shape-chip svg { width: 38px; height: 38px; flex-shrink: 0; }
.shape-chip span { font-size: 0.74rem; font-weight: 700; text-align: center; line-height: 1.15; }

/* ── Slider row ── */
.slider-row {
  display: flex; align-items: center; gap: 12px;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 10px; padding: 10px 14px;
  margin-bottom: 8px;
}
.slider-row .sim-slider-label {
  flex-shrink: 0; min-width: 110px; font-size: 0.82rem; font-weight: 700;
  color: var(--text-dim); display: flex; align-items: center; gap: 6px;
}
.slider-row .sim-slider-label .swatch {
  width: 12px; height: 12px; border-radius: 3px; display: inline-block;
}
.sim-slider {
  flex: 1; -webkit-appearance: none; appearance: none;
  height: 6px; background: rgba(255,255,255,.12);
  border-radius: 3px; outline: none;
  border: 1px solid rgba(255,255,255,.1);
}
.sim-slider::-webkit-slider-runnable-track {
  height: 6px; border-radius: 3px;
  background: linear-gradient(to right, var(--accent-lo), rgba(255,255,255,.12));
}
.sim-slider::-webkit-slider-thumb {
  -webkit-appearance: none; width: 18px; height: 18px; margin-top: -6px;
  border-radius: 50%; background: var(--accent); cursor: pointer;
  box-shadow: 0 0 8px var(--accent-lo);
  border: 2px solid rgba(255,255,255,.25);
}
.sim-slider::-moz-range-track {
  height: 6px; border-radius: 3px;
  background: linear-gradient(to right, var(--accent-lo), rgba(255,255,255,.12));
  border: none;
}
.sim-slider::-moz-range-thumb {
  width: 16px; height: 16px; border: 2px solid rgba(255,255,255,.25);
  border-radius: 50%; background: var(--accent); cursor: pointer;
}
.stepper {
  display: flex; align-items: center; gap: 0; min-width: 150px; flex-shrink: 0;
  border: 1px solid var(--border); border-radius: 8px; overflow: hidden;
  background: var(--bg); height: 36px;
}
.stepper-btn {
  width: 36px; height: 36px; border: none; background: var(--surface2);
  color: var(--text-dim); font-size: 1.1rem; font-weight: 700;
  cursor: pointer; display: flex; align-items: center; justify-content: center;
  transition: background .15s, color .15s; flex-shrink: 0;
  font-family: inherit;
}
.stepper-btn:hover { background: var(--accent-lo); color: var(--text); }
.stepper-btn:active { background: var(--accent); color: #fff; }
.stepper-val {
  flex: 1; font-family: var(--mono); font-size: 0.85rem; font-weight: 700;
  color: var(--accent); padding: 0 8px; white-space: nowrap; text-align: center;
  line-height: 36px; cursor: pointer;
}
.stepper-unit {
  font-size: 0.72rem; color: var(--text-dim); font-weight: 600;
  padding-right: 10px; white-space: nowrap;
}

/* ── Speed / Unit toggles ── */
.speed-strip { display: flex; align-items: center; gap: 6px; }

/* ── Canvas card ── */
.canvas-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 8px;
  margin-bottom: 12px;
  position: relative;
  overflow-x: clip;
  overflow-y: visible;
}
#main-canvas {
  width: 100%; height: auto; display: block;
  background: radial-gradient(ellipse at center, #131826 0%, #0a0d14 100%);
  border-radius: 8px;
  touch-action: none;
  cursor: crosshair;
}
#main-canvas.dragging { cursor: grabbing; }

/* ── Play / action bar ── */
.play-bar {
  display: flex; flex-wrap: wrap; gap: 10px; align-items: center;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 10px 14px; margin-bottom: 12px;
}
.play-btn {
  background: linear-gradient(135deg, var(--accent), var(--accent-3));
  border: none; color: #1a0a14;
  padding: 10px 22px; font-size: 0.95rem; font-weight: 800;
  border-radius: 10px; cursor: pointer;
  display: inline-flex; align-items: center; gap: 8px;
  box-shadow: 0 4px 18px var(--accent-lo);
  font-family: inherit;
  transition: transform .15s, box-shadow .15s;
}
.play-btn:hover { transform: translateY(-1px); box-shadow: 0 6px 24px rgba(255, 111, 177, 0.5); }
.play-btn:disabled { opacity: 0.55; cursor: not-allowed; transform: none; }
.play-icon { font-size: 0.85rem; }
.play-status {
  margin-left: auto; font-size: 0.82rem; color: var(--text-dim);
  font-family: var(--mono);
}

/* ── Readout badges ── */
.readout-badges {
  display: flex; flex-wrap: wrap; gap: 8px;
  margin-bottom: 12px;
}
.readout-badge {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 999px; padding: 6px 14px;
  font-size: 0.78rem; font-weight: 600;
  display: inline-flex; align-items: center; gap: 6px;
  color: var(--text-dim);
}
.readout-badge strong { color: var(--text); font-family: var(--mono); }
.rb-dot { width: 8px; height: 8px; border-radius: 50%; flex-shrink: 0; }

/* ── Formula panel ── */
.formula-panel {
  background: linear-gradient(135deg, var(--surface), var(--surface2));
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: var(--radius);
  padding: 14px 18px;
  margin-bottom: 12px;
  font-family: var(--mono);
  overflow-x: auto;
}
.formula-title {
  font-family: var(--font); font-size: 0.78rem; font-weight: 700;
  color: var(--text-dim); text-transform: uppercase; letter-spacing: 0.5px;
  margin-bottom: 8px;
}
.formula-row {
  display: flex; flex-wrap: wrap; align-items: center; gap: 8px;
  font-size: 1.05rem; font-weight: 700;
}
.f-label { color: var(--accent); font-weight: 800; }
.f-eq { color: var(--text-dim); }
.f-expr { color: var(--accent-2); }
.f-sub { color: var(--accent-3); }
.f-result {
  color: var(--accent-4); font-size: 1.15rem; font-weight: 800;
  background: rgba(149, 224, 108, 0.12);
  padding: 2px 10px; border-radius: 6px;
  border: 1px solid rgba(149, 224, 108, 0.3);
}
.step-narration {
  margin-top: 10px; padding-top: 10px; border-top: 1px dashed var(--border);
  font-family: var(--font); font-size: 0.88rem; color: var(--text);
}

/* ── Explore ── */
.explore-panel { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 16px; }
.explore-tabs { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 14px; border-bottom: 1px solid var(--border); padding-bottom: 10px; }
.explore-tab {
  border: 1px solid var(--border); background: var(--bg);
  color: var(--text-dim); padding: 8px 16px; font-size: 0.85rem; font-weight: 700;
  border-radius: 8px; cursor: pointer; font-family: inherit;
  transition: all .15s;
}
.explore-tab:hover { color: var(--text); border-color: var(--accent); }
.explore-tab.active {
  background: var(--accent-lo); color: var(--accent); border-color: var(--accent);
}
.explore-cards {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 14px;
}
.explore-card {
  background: var(--bg); border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: 10px; padding: 14px 16px;
}
.explore-card h4 { color: var(--accent); font-size: 0.98rem; margin-bottom: 8px; }
.explore-card p { font-size: 0.88rem; color: var(--text); margin-bottom: 8px; }
.explore-card .ec-formula {
  font-family: var(--mono); background: var(--surface2); border-radius: 6px;
  padding: 8px 10px; font-size: 0.92rem; color: var(--accent-2);
  border: 1px solid var(--border); margin-bottom: 8px;
}
.explore-card .ec-note {
  font-size: 0.8rem; color: var(--text-dim); font-style: italic;
  border-top: 1px dashed var(--border); padding-top: 6px;
}

/* ── Practice / Quiz ── */
.practice-panel, .quiz-panel, .quiz-result {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 18px;
}
.pq-prompt {
  font-size: 1rem; font-weight: 600; margin-bottom: 12px;
  padding: 12px 14px; background: var(--bg); border-radius: 8px;
  border-left: 3px solid var(--accent-3);
}
.pq-canvas-wrap {
  background: var(--bg); border: 1px solid var(--border);
  border-radius: 8px; padding: 8px; margin-bottom: 12px;
}
.pq-canvas-wrap canvas { width: 100%; height: auto; display: block; border-radius: 6px; }
.pq-answer {
  display: flex; flex-wrap: wrap; gap: 8px; align-items: center;
}
.pq-label { font-size: 0.88rem; color: var(--text-dim); font-weight: 600; }
.pq-input {
  background: var(--bg); border: 1px solid var(--border);
  color: var(--accent); font-family: var(--mono); font-weight: 700;
  font-size: 1rem; padding: 8px 12px; border-radius: 8px;
  width: 130px; outline: none; min-height: 36px;
}
.pq-input:focus { border-color: var(--accent); box-shadow: 0 0 0 2px var(--accent-lo); }
.pq-feedback { margin-top: 12px; padding: 10px 14px; border-radius: 8px; font-weight: 600; display: none; }
.pq-feedback.correct { background: rgba(61, 220, 132, 0.12); border: 1px solid var(--green); color: var(--green); display: block; }
.pq-feedback.wrong { background: rgba(255, 85, 85, 0.12); border: 1px solid var(--red); color: var(--red); display: block; }
.practice-score {
  margin-top: 12px; padding: 8px 14px; background: var(--bg);
  border-radius: 8px; font-size: 0.92rem; font-weight: 700;
  display: inline-block;
}
.quiz-head {
  display: flex; justify-content: space-between; align-items: center;
  margin-bottom: 14px; padding-bottom: 12px; border-bottom: 1px solid var(--border);
  font-size: 0.92rem; font-weight: 700;
}
.qz-actions { margin-top: 12px; display: flex; gap: 10px; flex-wrap: wrap; }
.qr-score-row { display: flex; flex-direction: column; align-items: center; gap: 10px; margin-bottom: 16px; }
.qr-stars { font-size: 2.2rem; }
.qr-score { font-size: 1.3rem; font-weight: 800; color: var(--accent); font-family: var(--mono); }
.qr-breakdown { margin-bottom: 14px; }
.qr-row { padding: 8px 12px; border-radius: 6px; margin-bottom: 6px; font-size: 0.88rem; }
.qr-row.ok { background: rgba(61, 220, 132, 0.1); }
.qr-row.no { background: rgba(255, 85, 85, 0.1); }

/* ── Context menu ── */
.ctx-menu {
  position: absolute; z-index: 100; min-width: 180px;
  background: var(--surface); border: 1px solid var(--border); border-radius: 8px;
  padding: 4px 0; box-shadow: 0 8px 24px rgba(0,0,0,.45);
}
.ctx-item {
  display: block; width: 100%; padding: 8px 16px; border: none;
  background: transparent; color: var(--text); font-size: 0.82rem;
  text-align: left; cursor: pointer; transition: background .12s;
  font-family: inherit;
}
.ctx-item:hover { background: var(--accent-lo); color: var(--accent); }

/* ── Real-world presets ── */
.preset-bar { padding: 8px 14px; }
.preset-chips { display: flex; flex-wrap: wrap; gap: 6px; }
.preset-chip {
  background: var(--bg); border: 1px solid var(--border);
  color: var(--text); padding: 4px 10px; font-size: 0.78rem;
  border-radius: 999px; cursor: pointer; font-family: inherit;
  transition: all .12s;
}
.preset-chip:hover { border-color: var(--accent); color: var(--accent); background: var(--accent-lo); }
.preset-chip:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* ── Inline editable stepper ── */
.stepper-input {
  flex: 1; border: none; background: transparent;
  color: var(--accent); font-family: var(--mono); font-weight: 700;
  font-size: 0.85rem; text-align: center;
  outline: none; height: 36px; width: 60px;
  -moz-appearance: textfield;
}
.stepper-input::-webkit-outer-spin-button,
.stepper-input::-webkit-inner-spin-button { -webkit-appearance: none; margin: 0; }

/* ── Triangle areas side panel (custom mode) ── */
.tri-panel {
  position: absolute;
  top: 12px; right: 12px;
  background: rgba(13, 17, 23, 0.92);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 8px 12px;
  font-family: var(--mono); font-size: 0.78rem;
  color: var(--text);
  max-width: 240px;
  pointer-events: none;
  box-shadow: 0 4px 16px rgba(0,0,0,0.4);
}
.tri-panel-title { font-family: var(--font); font-weight: 700; color: var(--accent); font-size: 0.78rem; margin-bottom: 6px; }
.tri-row {
  display: flex; justify-content: space-between; gap: 8px;
  padding: 2px 0; border-bottom: 1px dotted var(--border);
}
.tri-row:last-child { border-bottom: none; }
.tri-dot { width: 8px; height: 8px; border-radius: 50%; display: inline-block; margin-right: 4px; }
.tri-total { margin-top: 4px; padding-top: 4px; border-top: 1px solid var(--accent); color: var(--accent-4); font-weight: 700; }

/* ── Custom-draw helper bar ── */
.draw-help {
  background: var(--bg); border: 1px dashed var(--accent);
  border-radius: 8px; padding: 10px 14px; margin-bottom: 12px;
  font-size: 0.85rem; color: var(--text-dim);
}
.draw-help strong { color: var(--accent); }
.draw-help .draw-actions { margin-top: 6px; display: inline-flex; gap: 8px; flex-wrap: wrap; }
.draw-help .draw-actions .btn { padding: 4px 10px; min-height: 28px; font-size: 0.78rem; }

/* ── User guide ── */
.user-guide {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 22px 24px;
  margin-top: 24px;
}
.user-guide h2 {
  font-size: 1.4rem; color: var(--accent); margin-bottom: 14px;
  padding-bottom: 8px; border-bottom: 1px solid var(--border);
}
.user-guide details {
  border-bottom: 1px solid var(--border); padding: 10px 0;
}
.user-guide details:last-child { border-bottom: none; }
.user-guide summary {
  font-weight: 700; font-size: 0.96rem; cursor: pointer;
  padding: 4px 0; user-select: none;
  display: flex; align-items: center; gap: 10px;
}
.user-guide summary:hover { color: var(--accent); }
.user-guide .guide-section-num {
  display: inline-flex; align-items: center; justify-content: center;
  width: 24px; height: 24px;
  background: var(--accent-lo); color: var(--accent);
  border-radius: 50%; font-size: 0.78rem; font-weight: 800;
  flex-shrink: 0;
}
.user-guide details > *:not(summary) { margin-top: 8px; padding-left: 34px; font-size: 0.9rem; }
.user-guide ul { margin-left: 18px; }
.user-guide li { margin-bottom: 4px; }
.user-guide code { font-family: var(--mono); background: var(--bg); padding: 1px 6px; border-radius: 4px; color: var(--accent-2); }
.user-guide kbd { font-family: var(--mono); background: var(--bg); padding: 2px 8px; border-radius: 4px; border: 1px solid var(--border); color: var(--accent); font-size: 0.85em; }

/* ── SEO article ── */
.seo-article {
  margin-top: 36px; padding: 24px;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius);
  font-size: 0.92rem; line-height: 1.7;
}
.seo-article h2 { color: var(--accent); margin-bottom: 10px; font-size: 1.4rem; }
.seo-article h3 { color: var(--text); margin: 16px 0 8px; font-size: 1.08rem; }
.seo-article p { margin-bottom: 12px; color: var(--text); }
.seo-article a { color: var(--accent); text-decoration: none; border-bottom: 1px dotted var(--accent); }
.seo-article a:hover { color: var(--accent-3); border-bottom-color: var(--accent-3); }
.seo-article table {
  width: 100%; border-collapse: collapse; margin: 12px 0;
  font-size: 0.88rem;
}
.seo-article th, .seo-article td {
  padding: 8px 12px; border: 1px solid var(--border);
  text-align: left;
}
.seo-article th { background: var(--bg); color: var(--accent); font-weight: 700; }

/* ── Focus-visible ── */
.btn:focus-visible, .pill:focus-visible, .shape-chip:focus-visible, .stepper-btn:focus-visible, .play-btn:focus-visible, .ctx-item:focus-visible, .explore-tab:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ── Pulse animation for new triangle row ── */
@keyframes triPulse { 0% { background: var(--accent-lo); } 100% { background: transparent; } }
.tri-row.new { animation: triPulse 0.5s ease; }

/* ── Skip link ── */
.skip-link {
  position: absolute; left: -9999px; top: 0;
  background: var(--accent); color: #fff; padding: 8px 16px;
  font-weight: 700; z-index: 1000; border-radius: 0 0 8px 0;
}
.skip-link:focus { left: 0; }

/* ── Mode sections ── */
.mode-section { animation: fadeIn .25s ease; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(4px); } to { opacity: 1; transform: none; } }

/* ── Responsive ── */
@media (max-width: 768px) {
  #app { padding: 16px 14px 60px; }
  header h1 { font-size: 1.5rem; }
  .controls-bar { padding: 10px 12px; gap: 10px; }
  .slider-row { flex-wrap: wrap; }
  .slider-row .sim-slider-label { min-width: 100%; }
  .stepper { min-width: 130px; height: 44px; }
  .stepper-btn { width: 44px; height: 44px; }
  .stepper-val, .stepper-input { line-height: 44px; height: 44px; }
  .btn { min-height: 44px; }
  .shape-grid { grid-template-columns: repeat(auto-fill, minmax(92px, 1fr)); gap: 6px; }
  .shape-chip { padding: 8px 4px 6px; min-height: 60px; }
  .shape-chip svg { width: 32px; height: 32px; }
  .shape-chip span { font-size: 0.7rem; }
  .play-bar { padding: 8px 10px; }
  .play-status { margin-left: 0; width: 100%; }
  .tri-panel { max-width: 200px; font-size: 0.72rem; }
}
@media (max-width: 500px) {
  #app { padding: 12px 10px 50px; }
  header h1 { font-size: 1.3rem; }
  .pill { padding: 5px 10px; font-size: 0.78rem; }
  .play-btn { padding: 8px 16px; font-size: 0.88rem; }
  .formula-panel { padding: 10px 12px; }
  .formula-row { font-size: 0.92rem; }
  .f-result { font-size: 1rem; }
  .shape-grid { grid-template-columns: repeat(auto-fill, minmax(82px, 1fr)); }
  .explore-cards { grid-template-columns: 1fr; }
}