/* ═══════════════════════════════════════════════════════════
   Calculus Visualizer — Stylesheet
   ═══════════════════════════════════════════════════════════ */

:root {
  /* ── Background layers ── */
  --bg:        #0d1117;
  --surface:   #161b27;
  --surface2:  #1f2535;
  --border:    #2a3050;

  /* ── Accent — teal-green for calculus ── */
  --accent:    #00bfa5;
  --accent-lo: rgba(0,191,165,.22);

  /* ── Semantic colours — DO NOT CHANGE ── */
  --green:     #3ddc84;
  --red:       #ff5555;
  --gold:      #f5c842;

  /* ── Typography ── */
  --text:      #dde3f0;
  --text-dim:  #6b7a99;
  --font:      'Segoe UI', system-ui, sans-serif;
  --mono:      'Courier New', monospace;

  /* ── Layout ── */
  --radius:    12px;
}

/* ── Page Header ───────────────────────────────────────── */
header { text-align: center; padding: 10px 0 4px; }
header h1 {
  font-size: 1.8rem; font-weight: 700;
  background: linear-gradient(120deg, #00bfa5 0%, #64ffda 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.subtitle { color: var(--text-dim); font-size: 0.85rem; margin-top: 3px; }

/* ── Controls bar ──────────────────────────────────────── */
.controls-bar {
  display: flex; flex-wrap: wrap; align-items: center; gap: 14px;
  padding: 12px 16px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.ctrl-group { display: flex; align-items: center; gap: 8px; }
.ctrl-label { font-size: 0.72rem; text-transform: uppercase; letter-spacing: .06em; color: var(--text-dim); white-space: nowrap; }

/* ── Pill tabs ─────────────────────────────────────────── */
.pill-tabs { display: flex; background: var(--bg); border-radius: 8px; padding: 3px; gap: 2px; flex-wrap: wrap; }
.pill {
  padding: 8px 16px; border: none; background: transparent; color: var(--text-dim);
  border-radius: 6px; cursor: pointer; font-size: 0.81rem; min-height: 44px;
  transition: background .18s, color .18s, box-shadow .18s;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
  -webkit-user-select: none; user-select: none;
}
.pill.active { background: var(--accent); color: #fff; box-shadow: 0 0 12px var(--accent-lo); }
.pill:hover:not(.active) { background: var(--surface2); color: var(--text); }

/* ── Buttons ───────────────────────────────────────────── */
.btn {
  padding: 8px 18px; border: none; border-radius: 8px; cursor: pointer;
  font-size: 0.84rem; font-weight: 600; transition: filter .18s, box-shadow .18s, opacity .18s;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
}
.btn:disabled { opacity: 0.38; cursor: not-allowed; }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:not(:disabled):hover { filter: brightness(1.12); box-shadow: 0 0 12px var(--accent-lo); }
.btn-ghost { background: var(--surface2); color: var(--text); border: 1px solid var(--border); }
.btn-ghost:hover { background: var(--border); }

/* ── User Guide button ─────────────────────────────────── */
.btn-guide {
  margin-left: auto;
  padding: 6px 16px; border: none; border-radius: 8px; cursor: pointer;
  font-size: 0.82rem; font-weight: 700; text-decoration: none;
  background: var(--gold); color: #1a1a2e;
  transition: filter .18s, box-shadow .18s;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
}
.btn-guide:hover { filter: brightness(1.1); box-shadow: 0 0 14px rgba(245,200,66,.35); }

/* ── Hint bar ──────────────────────────────────────────── */
.hint-bar {
  display: flex; align-items: center; gap: 10px;
  padding: 10px 16px;
  background: var(--accent-lo); border: 1px solid rgba(0,191,165,.3);
  border-radius: var(--radius); font-size: 0.82rem; color: var(--text-dim);
}
.hint-text { flex: 1; line-height: 1.4; }
.hint-close {
  background: none; border: none; color: var(--text-dim); font-size: 1.3rem;
  cursor: pointer; padding: 4px 8px; border-radius: 4px; line-height: 1;
  transition: color .15s, background .15s;
  flex-shrink: 0;
}
.hint-close:hover { color: var(--text); background: rgba(255,255,255,.08); }

/* ── Focus visibility ──────────────────────────────────── */
.pill:focus-visible, .tb-btn:focus-visible, button:focus-visible, input:focus-visible {
  outline: 2px solid var(--accent); outline-offset: 2px;
}

/* ── Preset Bar ─────────────────────────────────────────── */
.preset-bar {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 0;
  margin-bottom: 12px;
  overflow-x: clip;
}
.preset-pills {
  display: flex;
  gap: 6px;
  overflow-x: auto;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
  padding-bottom: 4px;
}
.preset-pills::-webkit-scrollbar { height: 4px; }
.preset-pills::-webkit-scrollbar-track { background: transparent; }
.preset-pills::-webkit-scrollbar-thumb { background: var(--border); border-radius: 2px; }
.preset-pill {
  flex-shrink: 0;
  padding: 6px 14px;
  font-size: 0.82rem;
  border-radius: 20px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-dim);
  cursor: pointer;
  white-space: nowrap;
  transition: all .15s;
  min-height: 44px;
  display: flex;
  align-items: center;
}
.preset-pill:hover {
  border-color: var(--accent);
  color: var(--text);
}
.preset-pill.active {
  background: var(--accent-lo);
  border-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}

/* ── Simulator Panel (sidebar + canvas) ─────────────────── */
.sim-panel {
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 16px;
  min-height: 520px;
  margin-bottom: 24px;
}

/* ── Sidebar ────────────────────────────────────────────── */
.sidebar {
  display: flex;
  flex-direction: column;
  gap: 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  overflow-y: auto;
  max-height: 600px;
}
.sidebar-section { display: flex; flex-direction: column; gap: 8px; }
.sidebar-label {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

/* Expression input */
.expr-wrap { position: relative; }
.expr-input {
  width: 100%;
  padding: 10px 12px;
  font-family: var(--mono);
  font-size: 1rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  outline: none;
  transition: border-color .15s;
  box-sizing: border-box;
}
.expr-input:focus { border-color: var(--accent); }
.mkbd-trigger {
  width: 100%;
  display: flex; align-items: center; justify-content: center; gap: 7px;
  padding: 7px 12px;
  background: var(--surface2);
  border: 1px dashed var(--border);
  border-radius: 8px;
  color: var(--text-dim);
  font-size: 0.82rem;
  font-weight: 500;
  cursor: pointer;
  transition: color .15s, border-color .15s, background .15s;
  touch-action: manipulation;
}
.mkbd-trigger:hover {
  color: var(--accent);
  border-color: var(--accent);
  border-style: solid;
  background: var(--accent-lo);
}
.parse-error {
  font-size: 0.78rem;
  color: var(--red);
  min-height: 1.2em;
  margin: 0;
}

/* Action Buttons */
.action-buttons {
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.action-buttons .btn-differentiate,
.action-buttons .btn-integrate {
  width: 100%;
}

/* Integral limits row */
.integ-limits-row {
  display: flex;
  align-items: center;
  gap: 6px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 6px 10px;
}
.integ-limits-label {
  font-size: 0.82rem;
  color: var(--text-dim);
  white-space: nowrap;
  flex-shrink: 0;
}
.integ-limits-sep {
  font-size: 0.8rem;
  color: var(--text-dim);
  flex-shrink: 0;
}
.integ-limit-input {
  flex: 1;
  min-width: 0;
  padding: 4px 7px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text);
  font-size: 0.84rem;
  font-family: var(--mono);
  box-sizing: border-box;
  text-align: center;
}
.integ-limit-input:focus { border-color: var(--accent); outline: none; }
.integ-limit-input::placeholder { color: var(--text-dim); font-style: italic; }
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 16px;
  font-size: 0.88rem;
  font-weight: 600;
  border-radius: 8px;
  border: none;
  cursor: pointer;
  transition: all .15s;
  min-height: 44px;
  flex: 1;
}
.btn-differentiate {
  background: #ffd43b;
  color: #1a1a2e;
}
.btn-differentiate:hover { background: #ffe066; }
.btn-differentiate:active { transform: scale(0.97); }
.btn-integrate {
  background: var(--accent);
  color: #0d1117;
}
.btn-integrate:hover { background: #26d9b8; }
.btn-integrate:active { transform: scale(0.97); }
.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

/* Speed pills */
.speed-pills {
  display: flex;
  gap: 4px;
}
.speed-pills .pill { min-height: 44px; }

/* Progress bar */
.progress-bar-track {
  width: 100%;
  height: 6px;
  background: var(--surface2);
  border-radius: 3px;
  overflow: hidden;
}
.progress-bar-fill {
  height: 100%;
  width: 0%;
  background: var(--accent);
  border-radius: 3px;
  transition: width 0.05s linear;
}

/* Result & Analysis boxes */
.result-box, .analysis-box {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px;
  font-size: 0.88rem;
  color: var(--text);
  line-height: 1.5;
}
.result-box code, .analysis-box code {
  font-family: var(--mono);
  color: var(--accent);
}
.result-label {
  font-size: 0.75rem;
  color: var(--text-dim);
  margin-bottom: 4px;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}
.result-expr {
  font-size: 0.95rem;
  color: #ffd43b;
  word-break: break-all;
  line-height: 1.8;
}
.result-expr .katex { color: #ffd43b; font-size: 1.05rem; }
.result-rule {
  font-size: 0.78rem;
  color: var(--text-dim);
  margin-top: 6px;
  font-style: italic;
}

/* ── Analysis Chips ─────────────────────────────────────── */
.sb-analysis-grid { display: flex; flex-direction: column; gap: 10px; }
.sb-analysis-group { display: flex; flex-direction: column; gap: 5px; }
.sb-analysis-group.sb-analysis-yint {
  flex-direction: row; align-items: center; gap: 8px;
  padding: 6px 0; border-top: 1px solid rgba(42,48,80,.25);
}
.sb-analysis-header { display: flex; align-items: center; gap: 6px; }
.sb-analysis-key {
  color: var(--text-dim); font-size: 0.68rem; text-transform: uppercase;
  letter-spacing: .05em; font-weight: 600;
}
.sb-analysis-count {
  font-size: 0.6rem; font-weight: 700; color: var(--accent);
  background: var(--accent-lo); border-radius: 8px;
  padding: 1px 6px; min-width: 18px; text-align: center; line-height: 1.3;
}
.sb-analysis-chips {
  display: flex; flex-wrap: wrap; gap: 4px;
}
.sb-analysis-chip {
  display: inline-flex; align-items: center; justify-content: center; gap: 3px;
  padding: 3px 8px; border-radius: 6px;
  font-family: var(--mono); font-size: 0.72rem; line-height: 1.3;
  background: var(--surface2); border: 1px solid var(--border);
  color: var(--text); cursor: default;
  transition: background .12s, border-color .12s;
  text-align: center; white-space: nowrap;
  min-width: 0; max-width: 100%;
}
.sb-analysis-chip:hover {
  background: var(--accent-lo); border-color: var(--accent); cursor: pointer;
}
.sb-analysis-chip.active {
  background: var(--accent-lo); border-color: var(--accent);
  box-shadow: 0 0 8px var(--accent-lo);
}
.sb-analysis-chip.ext-max.active { border-color: var(--green); box-shadow: 0 0 8px rgba(61,220,132,.3); background: rgba(61,220,132,.12); }
.sb-analysis-chip.ext-min.active { border-color: var(--red); box-shadow: 0 0 8px rgba(255,85,85,.3); background: rgba(255,85,85,.12); }
.sb-analysis-chip.inflect.active { border-color: var(--gold); box-shadow: 0 0 8px rgba(245,200,66,.3); background: rgba(245,200,66,.12); }
.sb-analysis-chip.root { color: var(--accent); }
.sb-analysis-chip.ext-max { color: var(--green); border-color: rgba(61,220,132,.25); }
.sb-analysis-chip.ext-max::before { content: '\25B2'; font-size: 0.55rem; }
.sb-analysis-chip.ext-min { color: var(--red); border-color: rgba(255,85,85,.25); }
.sb-analysis-chip.ext-min::before { content: '\25BC'; font-size: 0.55rem; }
.sb-analysis-chip.inflect { color: var(--gold); border-color: rgba(245,200,66,.2); }
.sb-analysis-chip.yint { color: var(--accent); font-weight: 600; }
.sb-analysis-chip.integ { color: #51cf66; border-color: rgba(81,207,102,.25); }
.sb-analysis-none { font-size: 0.75rem; color: var(--text-dim); font-style: italic; }

/* ── Math Keyboard Modal ────────────────────────────────── */
.mkbd-overlay {
  position: fixed; inset: 0; z-index: 600;
  background: rgba(0,0,0,.65); backdrop-filter: blur(4px);
  display: flex; align-items: center; justify-content: center;
  padding: 16px;
  box-sizing: border-box;
}
.mkbd-dialog {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  width: 100%; max-width: 480px;
  max-height: 90vh;
  overflow-y: auto;
  box-shadow: 0 16px 48px rgba(0,0,0,.55);
  display: flex; flex-direction: column;
  box-sizing: border-box;
}
/* Mobile: bottom sheet */
@media (max-width: 500px) {
  .mkbd-overlay { align-items: flex-end; padding: 0; }
  .mkbd-dialog {
    max-width: 100%; width: 100%;
    max-height: 85vh; border-radius: 18px 18px 0 0;
    border-bottom: none;
  }
}

/* Header */
.mkbd-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 16px 10px;
  border-bottom: 1px solid var(--border);
}
.mkbd-title { font-size: 0.95rem; font-weight: 600; color: var(--text); }
.mkbd-close {
  width: 30px; height: 30px; border-radius: 8px;
  background: transparent; border: 1px solid transparent;
  color: var(--text-dim); font-size: 1.2rem; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: all .15s; padding: 0;
}
.mkbd-close:hover { background: rgba(255,85,85,.15); border-color: rgba(255,85,85,.3); color: #ff5555; }

/* KaTeX preview bar */
.mkbd-preview {
  min-height: 54px;
  background: var(--surface2);
  margin: 10px 12px 0;
  border-radius: 10px;
  padding: 10px 16px;
  font-size: 1.25rem;
  color: var(--gold);
  display: flex; align-items: center;
  overflow-x: auto;
  border: 1px solid var(--border);
}
.mkbd-preview .katex { color: var(--gold); font-size: 1.15rem; }
.mkbd-preview-placeholder { color: var(--text-dim); font-style: italic; font-size: 0.9rem; }
.mkbd-preview-raw { font-family: var(--mono); font-size: 0.95rem; color: var(--text-dim); }

/* Expression input row */
.mkbd-input-row {
  display: flex; align-items: center; gap: 6px;
  padding: 8px 12px 4px;
}
.mkbd-input {
  flex: 1; padding: 8px 12px;
  font-family: var(--mono); font-size: 0.95rem;
  background: var(--surface2); border: 1px solid var(--border);
  border-radius: 8px; color: var(--text); outline: none;
  transition: border-color .15s; min-width: 0;
}
.mkbd-input:focus { border-color: var(--accent); }

/* Tab bar */
.mkbd-tabs {
  display: flex; margin: 8px 12px 0;
  border-radius: 10px; overflow: hidden;
  border: 1px solid var(--border);
}
.mkbd-tab {
  flex: 1; min-height: 38px; padding: 0 8px;
  background: var(--surface2); border: none; border-right: 1px solid var(--border);
  color: var(--text-dim); font-size: 0.82rem; font-weight: 500;
  cursor: pointer; transition: all .15s;
}
.mkbd-tab:last-child { border-right: none; }
.mkbd-tab:hover { color: var(--text); background: var(--surface); }
.mkbd-tab.active {
  background: var(--accent-lo); color: var(--accent);
  border-bottom: 2px solid var(--accent);
}

/* Tab panels */
.mkbd-panel { display: none; padding: 10px 12px 4px; }
.mkbd-panel.active { display: block; }

/* Button grids */
.mkbd-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 6px;
}
.mkbd-grid-3 {
  grid-template-columns: repeat(3, 1fr);
}

/* All keyboard buttons — touch-friendly */
.mkbd-btn {
  min-height: 48px; min-width: 0;
  border-radius: 10px; border: 1px solid var(--border);
  background: var(--surface2); color: var(--text);
  font-size: 0.9rem; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: background .12s, border-color .12s, transform .08s;
  padding: 4px 6px; font-family: var(--font);
  -webkit-tap-highlight-color: transparent;
  user-select: none;
}
.mkbd-btn:hover { border-color: var(--accent); color: var(--accent); background: rgba(0,191,165,.08); }
.mkbd-btn:active { transform: scale(0.93); background: var(--accent-lo); }

/* Number buttons — slightly brighter */
.mkbd-btn-num { background: var(--surface); font-size: 1rem; font-weight: 600; }

/* Constant buttons (π, e) */
.mkbd-btn-const { color: #c084fc; border-color: rgba(192,132,252,.25); font-size: 1.05rem; }
.mkbd-btn-const:hover { color: #c084fc; border-color: #c084fc; background: rgba(192,132,252,.12); }

/* Variable x button */
.mkbd-btn-var { color: var(--accent); border-color: var(--accent-lo); font-weight: 700; font-size: 1rem; }
.mkbd-btn-var:hover { background: var(--accent-lo); }

/* Operator buttons */
.mkbd-btn-op { color: #74c0fc; border-color: rgba(116,192,252,.2); }
.mkbd-btn-op:hover { color: #74c0fc; border-color: #74c0fc; background: rgba(116,192,252,.1); }

/* Function buttons */
.mkbd-btn-fn { color: var(--gold); border-color: rgba(245,200,66,.2); font-size: 0.82rem; }
.mkbd-btn-fn:hover { color: var(--gold); border-color: var(--gold); background: rgba(245,200,66,.1); }

/* Hyperbolic sub-style */
.mkbd-btn-hyp { color: #ffa94d; border-color: rgba(255,169,77,.2); }
.mkbd-btn-hyp:hover { color: #ffa94d; border-color: #ffa94d; background: rgba(255,169,77,.1); }

/* DEL + CLR */
.mkbd-btn-del { color: #ff8787; border-color: rgba(255,135,135,.2); min-width: 48px; font-size: 1rem; }
.mkbd-btn-del:hover { color: #ff5555; border-color: #ff5555; background: rgba(255,85,85,.1); }
.mkbd-btn-clr { color: var(--text-dim); min-width: 48px; font-size: 0.78rem; letter-spacing: .03em; }

/* Operator strip */
.mkbd-ops {
  display: flex; flex-wrap: wrap; gap: 6px;
  padding: 8px 12px;
  border-top: 1px solid var(--border);
  margin-top: 4px;
}
.mkbd-ops .mkbd-btn { flex: 1; min-width: 36px; min-height: 44px; }

/* Action row */
.mkbd-actions {
  display: flex; gap: 10px; padding: 10px 12px 14px;
  border-top: 1px solid var(--border);
  margin-top: 4px;
}
.mkbd-actions .btn { flex: 1; min-height: 44px; font-size: 0.9rem; }
.mkbd-apply-btn {
  background: var(--accent); color: #0d1117;
  border: none; border-radius: 10px; font-weight: 700; cursor: pointer;
  transition: opacity .15s, transform .08s;
}
.mkbd-apply-btn:hover { opacity: 0.88; }
.mkbd-apply-btn:active { transform: scale(0.97); }

/* ── KaTeX overrides ────────────────────────────────────── */
/* Preset pills: keep math compact so pills don't grow tall */
.preset-pill .katex { font-size: 0.88rem; }
.preset-pill .katex-display { display: inline; margin: 0; }
/* Integral result: slightly larger, inherits yellow */
.result-expr .katex-display { display: inline; margin: 0; }

/* ── Annotation Tool Bar ────────────────────────────────── */
.tool-bar {
  display: flex; gap: 6px; padding: 6px 8px; align-items: center;
  background: var(--surface2); border-bottom: 1px solid var(--border);
  border-radius: var(--radius) var(--radius) 0 0;
  overflow-x: auto; -webkit-overflow-scrolling: touch;
}
.tool-btn {
  padding: 8px 14px; border: 1px solid var(--border); border-radius: 8px;
  background: transparent; color: var(--text-dim); font-size: 0.82rem;
  cursor: pointer; transition: all .15s; white-space: nowrap;
  min-height: 44px;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
  -webkit-user-select: none; user-select: none;
}
.tool-btn:hover { background: var(--surface); color: var(--text); border-color: var(--accent); }
.tool-btn.active { background: var(--accent); color: #fff; border-color: var(--accent); }

.tool-btn-group { position: relative; display: flex; flex-shrink: 0; }
.tool-btn-group .tool-btn-sketch {
  border-top-right-radius: 0; border-bottom-right-radius: 0; border-right: none;
}
.tool-btn-drop {
  padding: 8px 8px; border: 1px solid var(--border); border-radius: 0 8px 8px 0;
  background: transparent; color: var(--text-dim); font-size: 0.78rem;
  cursor: pointer; transition: all .15s; min-height: 44px;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
  -webkit-user-select: none; user-select: none;
  display: flex; align-items: center;
}
.tool-btn-drop:hover { background: var(--surface); color: var(--text); }
.tool-btn-group .tool-btn-sketch.active ~ .tool-btn-drop,
.tool-btn-group .tool-btn-sketch.active + .tool-btn-drop {
  background: var(--accent); color: #fff; border-color: var(--accent);
}

.tool-btn-sketch::after {
  content: ''; display: inline-block; width: 8px; height: 8px;
  border-radius: 50%; margin-left: 5px; vertical-align: middle;
  background: var(--sketch-color, #fff); border: 1px solid rgba(255,255,255,.3);
  flex-shrink: 0;
}

.sketch-dropdown {
  position: absolute; top: calc(100% + 4px); left: 0; z-index: 300;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 10px; padding: 10px 12px; min-width: 180px;
  box-shadow: 0 6px 24px rgba(0,0,0,.4);
}
.sketch-dd-label {
  font-size: 0.68rem; color: var(--text-dim); text-transform: uppercase;
  letter-spacing: 0.05em; margin-bottom: 6px; margin-top: 4px;
}
.sketch-dd-label:first-child { margin-top: 0; }
.sketch-colors { display: flex; gap: 6px; margin-bottom: 8px; }
.swatch {
  width: 28px; height: 28px; border-radius: 50%; border: 2px solid var(--border);
  cursor: pointer; transition: all .15s; flex-shrink: 0;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
}
.swatch:hover { transform: scale(1.15); }
.swatch.active { border-color: var(--accent); box-shadow: 0 0 0 2px var(--accent); }
.sketch-widths { display: flex; gap: 6px; }
.width-btn {
  flex: 1; padding: 6px 0; border: 1px solid var(--border); border-radius: 6px;
  background: transparent; color: var(--text-dim); cursor: pointer;
  transition: all .15s; display: flex; align-items: center; justify-content: center;
  min-height: 32px;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
}
.width-btn:hover { background: var(--surface2); color: var(--text); }
.width-btn.active { background: var(--accent); color: #fff; border-color: var(--accent); }
.wline { display: block; border-radius: 2px; background: currentColor; }
.wline-thin  { width: 20px; height: 2px; }
.wline-med   { width: 20px; height: 4px; }
.wline-thick { width: 20px; height: 7px; }

.tool-btn-action { border-color: rgba(211,47,47,.3); color: var(--text-dim); }
.tool-btn-action:hover {
  background: rgba(211,47,47,.12); color: #ff6b6b; border-color: rgba(211,47,47,.5);
}

.tool-btn-shape::after {
  content: ''; display: inline-block; width: 8px; height: 8px;
  border-radius: 50%; margin-left: 5px; vertical-align: middle;
  background: var(--shape-color, #fff); border: 1px solid rgba(255,255,255,.3);
  flex-shrink: 0;
}
.tool-btn-group .tool-btn-shape {
  border-top-right-radius: 0; border-bottom-right-radius: 0; border-right: none;
}
.tool-btn-group .tool-btn-shape.active ~ .tool-btn-drop,
.tool-btn-group .tool-btn-shape.active + .tool-btn-drop {
  background: var(--accent); color: #fff; border-color: var(--accent);
}
.shape-dropdown {
  position: absolute; top: calc(100% + 4px); left: 0; z-index: 300;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 10px; padding: 10px 12px; min-width: 200px;
  box-shadow: 0 6px 24px rgba(0,0,0,.4);
}
.shape-picker {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 4px; margin-bottom: 8px;
}
.shape-pick {
  padding: 6px 0; border: 1px solid var(--border); border-radius: 6px;
  background: transparent; color: var(--text-dim); cursor: pointer;
  font-size: 1rem; text-align: center; transition: all .15s;
  min-height: 34px;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
}
.shape-pick:hover { background: var(--surface2); color: var(--text); }
.shape-pick.active { background: var(--accent); color: #fff; border-color: var(--accent); }
.shape-fill-row { display: flex; gap: 6px; }
.fill-btn {
  flex: 1; padding: 6px 0; border: 1px solid var(--border); border-radius: 6px;
  background: transparent; color: var(--text-dim); cursor: pointer;
  font-size: 0.78rem; transition: all .15s; text-align: center;
  touch-action: manipulation; -webkit-tap-highlight-color: transparent;
}
.fill-btn:hover { background: var(--surface2); color: var(--text); }
.fill-btn.active { background: var(--accent); color: #fff; border-color: var(--accent); }

.shape-text-input {
  position: absolute; z-index: 50; padding: 4px 8px;
  background: rgba(13,17,23,.9); border: 1px solid var(--accent);
  border-radius: 6px; color: #fff; font-size: 13px;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  outline: none; min-width: 80px; max-width: 220px;
}

/* ── Clear Confirmation Dialog ──────────────────────────── */
.confirm-overlay {
  position: absolute; inset: 0; z-index: 200;
  background: rgba(0,0,0,.55); backdrop-filter: blur(3px);
  display: flex; align-items: center; justify-content: center;
}
.confirm-dialog {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 12px; padding: 20px 24px; max-width: 320px; width: 90%;
  text-align: center; box-shadow: 0 8px 32px rgba(0,0,0,.4);
}
.confirm-icon { font-size: 2rem; margin-bottom: 8px; }
.confirm-title {
  font-size: 1rem; font-weight: 700; color: var(--text); margin-bottom: 6px;
}
.confirm-msg {
  font-size: 0.8rem; color: var(--text-dim); line-height: 1.45; margin-bottom: 16px;
}
.clear-select {
  width: 100%; padding: 10px 12px; margin: 10px 0 6px;
  background: var(--surface2); border: 1px solid var(--border); border-radius: 8px;
  color: var(--text); font-size: 0.85rem; font-family: var(--font);
  cursor: pointer; appearance: auto; outline: none;
}
.clear-select:focus { border-color: var(--accent); }
.clear-hint {
  font-size: 0.7rem; color: var(--text-dim); text-align: center;
  margin-bottom: 12px; line-height: 1.4; min-height: 2em;
}
.confirm-actions { display: flex; gap: 10px; justify-content: center; }
.confirm-actions .btn { flex: 1; padding: 8px 0; font-size: 0.82rem; border-radius: 8px; cursor: pointer; }
.btn-ghost { background: var(--surface2); color: var(--text); border: 1px solid var(--border); }
.btn-ghost:hover { background: var(--border); }
.btn-danger { background: #d32f2f; color: #fff; border: none; font-weight: 600; }
.btn-danger:hover { background: #b71c1c; }

/* ── Canvas Wrap ────────────────────────────────────────── */
.canvas-wrap {
  position: relative;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  min-height: 400px;
}
.canvas-wrap canvas {
  display: block;
  width: 100%;
  height: auto;
  touch-action: none;
  cursor: crosshair;
}
.canvas-wrap.fullscreen {
  position: fixed;
  inset: 0;
  z-index: 9999;
  border-radius: 0;
  border: none;
  min-height: auto;
}

/* Canvas toolbar (positioned below tool-bar) */
.canvas-toolbar {
  position: absolute;
  top: 52px;
  right: 8px;
  display: flex;
  gap: 4px;
  z-index: 10;
}
.tb-btn {
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(22,27,39,0.85);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text-dim);
  cursor: pointer;
  transition: all .15s;
  min-width: 44px;
  min-height: 44px;
}
.tb-btn:hover {
  background: var(--surface2);
  color: var(--text);
  border-color: var(--accent);
}

/* Floating label */
.floating-label {
  position: absolute;
  padding: 4px 10px;
  font-size: 0.82rem;
  font-family: var(--mono);
  background: rgba(22,27,39,0.9);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text);
  pointer-events: none;
  white-space: nowrap;
  z-index: 5;
}

/* ── Explore Mode ──────────────────────────────────────── */
.explore-wrapper { margin-bottom: 24px; }
.explore-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 14px;
}
.concept-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
  transition: border-color .15s, transform .15s;
  cursor: default;
}
.concept-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.concept-card-name {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 4px;
}
.concept-card-formula {
  font-family: var(--mono);
  font-size: 0.88rem;
  color: var(--accent);
  margin-bottom: 8px;
}
.concept-card-desc {
  font-size: 0.82rem;
  color: var(--text-dim);
  line-height: 1.5;
  margin-bottom: 8px;
}
.concept-card-example {
  font-size: 0.78rem;
  color: var(--text-dim);
  background: var(--surface2);
  border-radius: 6px;
  padding: 8px 10px;
  font-family: var(--mono);
  line-height: 1.4;
}

/* ── Practice Mode ─────────────────────────────────────── */
.practice-wrapper { margin-bottom: 24px; }
.practice-panel {
  max-width: 600px;
  margin: 0 auto;
}
.practice-problem {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 16px;
  text-align: center;
}
.practice-problem-label {
  font-size: 0.75rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 8px;
}
.practice-problem-text {
  font-size: 1.15rem;
  font-family: var(--mono);
  color: var(--text);
  line-height: 1.6;
  margin-bottom: 16px;
}
.practice-input-row {
  display: flex;
  gap: 8px;
  justify-content: center;
  align-items: center;
}
.practice-input {
  width: 200px;
  padding: 10px 14px;
  font-family: var(--mono);
  font-size: 1rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  outline: none;
  text-align: center;
}
.practice-input:focus { border-color: var(--accent); }
.practice-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 20px;
  font-size: 0.88rem;
  font-weight: 600;
  border-radius: 8px;
  border: none;
  cursor: pointer;
  transition: all .15s;
  min-height: 44px;
  background: var(--accent);
  color: #0d1117;
}
.practice-btn:hover { background: #26d9b8; }
.practice-btn.secondary {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text);
}
.practice-btn.secondary:hover { border-color: var(--accent); }
.practice-feedback {
  margin-top: 14px;
  padding: 12px;
  border-radius: 8px;
  font-size: 0.9rem;
  line-height: 1.5;
}
.practice-feedback.correct {
  background: rgba(61,220,132,.12);
  border: 1px solid var(--green);
  color: var(--green);
}
.practice-feedback.wrong {
  background: rgba(255,85,85,.12);
  border: 1px solid var(--red);
  color: var(--red);
}
.practice-score {
  text-align: center;
  font-size: 0.82rem;
  color: var(--text-dim);
  margin-top: 8px;
}
.practice-actions {
  display: flex;
  gap: 8px;
  justify-content: center;
  margin-top: 12px;
}

/* ── Quiz Mode ─────────────────────────────────────────── */
.quiz-wrapper { margin-bottom: 24px; }
.quiz-panel {
  max-width: 600px;
  margin: 0 auto;
}
.quiz-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
  padding: 12px 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}
.quiz-header-item {
  font-size: 0.85rem;
  color: var(--text-dim);
}
.quiz-header-item strong { color: var(--text); }
.quiz-timer { font-family: var(--mono); color: var(--accent); font-weight: 700; }
.quiz-question {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 16px;
}
.quiz-q-label {
  font-size: 0.75rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 8px;
}
.quiz-q-text {
  font-size: 1.05rem;
  color: var(--text);
  line-height: 1.5;
  margin-bottom: 16px;
}
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-option {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  transition: all .15s;
  min-height: 44px;
  font-size: 0.92rem;
  color: var(--text);
}
.quiz-option:hover { border-color: var(--accent); }
.quiz-option.selected { border-color: var(--accent); background: var(--accent-lo); }
.quiz-option.correct { border-color: var(--green); background: rgba(61,220,132,.12); color: var(--green); }
.quiz-option.wrong { border-color: var(--red); background: rgba(255,85,85,.12); color: var(--red); }
.quiz-option-letter {
  width: 28px;
  height: 28px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  background: var(--surface);
  border: 1px solid var(--border);
  font-size: 0.78rem;
  font-weight: 700;
  flex-shrink: 0;
}
.quiz-actions {
  display: flex;
  gap: 8px;
  justify-content: center;
  margin-top: 12px;
}
.quiz-results {
  text-align: center;
  padding: 32px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}
.quiz-results h2 { margin: 0 0 8px; font-size: 1.3rem; }
.quiz-results .score-big {
  font-size: 3rem;
  font-weight: 700;
  color: var(--accent);
  margin: 16px 0;
}
.quiz-results .score-label {
  font-size: 0.88rem;
  color: var(--text-dim);
  margin-bottom: 20px;
}

/* ── User Guide ─────────────────────────────────────────── */
.user-guide {
  margin: 32px 0;
}
.user-guide h2 {
  font-size: 1.2rem;
  margin-bottom: 12px;
}
.user-guide details {
  margin-bottom: 4px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}
.user-guide summary {
  padding: 12px 16px;
  font-weight: 600;
  cursor: pointer;
  color: var(--text);
  min-height: 44px;
  display: flex;
  align-items: center;
}
.user-guide summary:hover { background: var(--surface2); }
.user-guide details[open] summary { border-bottom: 1px solid var(--border); }
.user-guide details p {
  padding: 12px 16px;
  margin: 0;
  color: var(--text-dim);
  line-height: 1.6;
}
.user-guide code {
  font-family: var(--mono);
  font-size: 0.88em;
  color: var(--accent);
  background: var(--surface2);
  padding: 1px 5px;
  border-radius: 4px;
}

/* ══════════════════════════════════════════════════════════
   RESPONSIVE
   ══════════════════════════════════════════════════════════ */

@media (max-width: 768px) {
  .sim-panel {
    grid-template-columns: 1fr;
    min-height: auto;
  }
  .sidebar {
    max-height: none;
    order: -1;
  }
  .canvas-wrap { min-height: 350px; }
  .preset-bar { flex-wrap: wrap; }
  .tool-bar { gap: 6px; padding: 8px 10px; }
}

@media (max-width: 500px) {
  .action-buttons { flex-direction: column; }
  .canvas-wrap { min-height: 280px; }
  .sim-panel { gap: 10px; }
  .sidebar { padding: 12px; }
  .tool-btn { padding: 6px 10px; font-size: 0.76rem; min-height: 40px; }
  .tool-bar { gap: 4px; padding: 6px 8px; overflow-x: auto; -webkit-overflow-scrolling: touch; }
}

/* Result limits hint */
.result-limits-hint {
  font-size: 0.72rem;
  color: var(--text-dim);
  text-align: center;
  margin-top: 4px;
  font-style: italic;
}

/* ── Parameter Sliders ──────────────────────────────────── */
.params-panel {
  display: flex;
  flex-direction: column;
  gap: 10px;
  padding: 10px 12px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 10px;
}
.params-panel::before {
  content: 'Parameters';
  font-size: 0.72rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--text-dim);
}
.param-row { display: flex; flex-direction: column; gap: 4px; }
.param-top {
  display: flex;
  align-items: center;
  gap: 8px;
}
.param-label {
  font-family: var(--mono);
  font-size: 0.92rem;
  font-weight: 700;
  color: var(--gold);
  min-width: 20px;
  flex-shrink: 0;
}
.param-slider {
  flex: 1;
  height: 4px;
  accent-color: var(--accent);
  cursor: pointer;
  min-height: 22px;
}
.param-value {
  font-family: var(--mono);
  font-size: 0.82rem;
  color: var(--text);
  min-width: 40px;
  text-align: right;
  flex-shrink: 0;
}
.param-play-btn {
  width: 30px; height: 30px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  color: var(--text-dim);
  cursor: pointer;
  font-size: 0.7rem;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0;
  transition: color .15s, border-color .15s, background .15s;
  touch-action: manipulation;
}
.param-play-btn:hover { color: var(--accent); border-color: var(--accent); }
.param-play-btn.playing { color: var(--red); border-color: var(--red); background: rgba(255,85,85,.12); }
.param-limits {
  display: flex;
  align-items: center;
  gap: 6px;
  padding-left: 28px;
}
.param-limits-label { font-size: 0.7rem; color: var(--text-dim); }
.param-limits-sep { font-size: 0.7rem; color: var(--text-dim); }
.param-min, .param-max {
  width: 54px;
  padding: 3px 6px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 5px;
  color: var(--text-dim);
  font-size: 0.76rem;
  font-family: var(--mono);
  box-sizing: border-box;
}
.param-min:focus, .param-max:focus { border-color: var(--accent); outline: none; }