*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --bg: #0d1117; --surface: #161b27; --surface2: #1f2535; --border: #2a3050;
  --accent: #ff6e40; --accent-lo: rgba(255,110,64,.22);
  --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 { background: var(--bg); color: var(--text); font-family: var(--font); }
#app { max-width: 960px; margin: 0 auto; padding: 16px 20px 60px; }

/* ─── Header ─── */
header { text-align: center; margin: 12px 0 18px; }
h1 { font-size: 1.85rem; background: linear-gradient(135deg, var(--accent), #ffab91); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.subtitle { color: var(--text-dim); font-size: .92rem; margin-top: 4px; }

/* ─── Controls bar ─── */
.controls-bar { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; margin-bottom: 14px; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 12px 16px; }
.ctrl-group { display: flex; align-items: center; gap: 8px; }
.ctrl-label { font-size: .72rem; text-transform: uppercase; letter-spacing: .06em; color: var(--text-dim); white-space: nowrap; font-weight: 600; }
.pill-tabs { display: flex; background: var(--bg); border-radius: 8px; padding: 3px; gap: 2px; }
.pill { border: none; background: transparent; color: var(--text-dim); padding: 6px 14px; border-radius: 6px; font-size: .82rem; font-weight: 600; cursor: pointer; transition: all .15s; }
.pill:hover { background: var(--surface2); color: var(--text); }
.pill.active { background: var(--accent); color: #fff; box-shadow: 0 2px 10px var(--accent-lo); }

/* ─── Canvas card ─── */
.canvas-card { position: relative; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 8px; margin-bottom: 14px; overflow-x: clip; }
#sim-canvas { display: block; width: 100%; height: auto; border-radius: 8px; background: #0a0e18; touch-action: none; cursor: crosshair; }
.canvas-actions { position: absolute; bottom: 14px; left: 14px; display: flex; align-items: center; gap: 6px; z-index: 10; }
.btn-sm { padding: 5px 12px; font-size: .78rem; border-radius: 6px; }
.canvas-actions .live-toggle { margin-left: 4px; }

/* ─── Context menu ─── */
.ctx-menu { position: absolute; z-index: 100; min-width: 160px; background: var(--surface); border: 1px solid var(--border); border-radius: 8px; padding: 4px 0; box-shadow: 0 8px 24px rgba(0,0,0,.4); }
.ctx-item { display: block; width: 100%; padding: 8px 16px; border: none; background: transparent; color: var(--text); font-size: .82rem; text-align: left; cursor: pointer; transition: background .12s; }
.ctx-item:hover { background: var(--accent-lo); color: var(--accent); }

/* ─── Readout badges ─── */
.readout-badges { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 14px; }
.readout-badge { display: flex; align-items: center; gap: 6px; background: var(--surface); border: 1px solid var(--border); border-radius: 20px; padding: 5px 14px; font-size: .78rem; color: var(--text-dim); }
.readout-badge strong { color: var(--accent); font-family: var(--mono); font-size: .88rem; }
.rb-dot { width: 8px; height: 8px; border-radius: 50%; flex-shrink: 0; }

/* ─── Sim controls ─── */
.sim-controls { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 14px; margin-bottom: 14px; }
.slider-row { display: flex; align-items: center; gap: 10px; width: 100%; margin-bottom: 10px; }
.slider-row:last-of-type { margin-bottom: 0; }
.sim-slider-label { flex-shrink: 0; min-width: 110px; font-size: .82rem; color: var(--text-dim); font-weight: 600; }

/* ─── Sliders ─── */
.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); min-width: 80px; }
.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,.2); }
.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,.2); border-radius: 50%; background: var(--accent); cursor: pointer; }

/* ─── Steppers ─── */
.stepper { display: flex; align-items: center; gap: 0; min-width: 160px; 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; }
.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: .85rem; font-weight: 700; color: var(--accent); padding: 0 8px; white-space: nowrap; text-align: center; line-height: 36px; cursor: pointer; }
.stepper-val:hover { text-decoration: underline dashed var(--accent); }
.stepper-unit { font-size: .75rem; color: var(--text-dim); font-weight: 600; padding-right: 10px; white-space: nowrap; }

/* ─── Preset row ─── */
.preset-row { display: flex; align-items: center; gap: 8px; margin-bottom: 14px; flex-wrap: wrap; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 10px 14px; }
.preset-row .sim-slider-label { font-size: .78rem; color: var(--text-dim); font-weight: 700; margin-right: 4px; }
.preset-btn { padding: 7px 16px !important; font-size: .8rem !important; border-radius: 8px; }
.preset-btn:hover { border-color: var(--accent); color: var(--accent); }

/* ─── Live toggle ─── */
.live-toggle { display: flex; align-items: center; gap: 6px; cursor: pointer; font-size: .82rem; color: var(--text-dim); margin-left: auto; user-select: none; }
.live-toggle input { accent-color: var(--accent); width: 16px; height: 16px; cursor: pointer; }
.live-toggle span { font-weight: 600; }

/* ─── Action bar ─── */
.action-bar { display: flex; align-items: center; gap: 8px; margin-top: 14px; }
.btn { border: none; padding: 8px 18px; border-radius: 8px; font-size: .85rem; font-weight: 600; cursor: pointer; transition: all .15s; }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { filter: brightness(1.15); }
.btn-ghost { background: var(--surface2); color: var(--text-dim); border: 1px solid var(--border); }
.btn-ghost:hover { color: var(--text); border-color: var(--accent); }

/* ─── Formula row ─── */
.formula-row { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 10px 16px; margin-bottom: 14px; font-family: var(--mono); font-size: .85rem; }
.formula-label { color: var(--gold); font-weight: 700; }
.formula-eq { color: var(--text-dim); }
.formula-expr { color: var(--text); }
.formula-result { color: var(--accent); font-weight: 700; }

/* ─── Info row ─── */
.info-row { display: grid; grid-template-columns: repeat(auto-fit, minmax(130px, 1fr)); gap: 8px; margin-bottom: 18px; }
.info-cell { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 10px 14px; text-align: center; }
.info-label { display: block; font-size: .68rem; text-transform: uppercase; letter-spacing: .06em; color: var(--text-dim); margin-bottom: 4px; }
.info-val { display: block; font-family: var(--mono); font-size: 1.05rem; font-weight: 700; color: var(--accent); }

/* ─── Result description ─── */
.result-description { background: var(--surface); border: 1px solid var(--border); border-left: 3px solid var(--accent); border-radius: var(--radius); padding: 14px 18px; margin-bottom: 18px; }
.result-description p { font-size: .9rem; line-height: 1.6; color: var(--text-dim); }
.result-description strong { color: var(--accent); }
.result-description .desc-highlight { color: var(--green); font-weight: 600; }

/* ─── 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; }
.explore-tab { border: 1px solid var(--border); background: var(--surface2); color: var(--text-dim); padding: 6px 14px; border-radius: 8px; font-size: .82rem; font-weight: 600; cursor: pointer; transition: all .15s; }
.explore-tab:hover { color: var(--text); border-color: var(--accent); }
.explore-tab.active { background: var(--accent); color: #fff; border-color: var(--accent); }
.explore-cards { display: grid; gap: 12px; }
.explore-card { background: var(--bg); border: 1px solid var(--border); border-radius: 10px; padding: 16px; }
.explore-card h3 { font-size: .95rem; color: var(--accent); margin-bottom: 8px; }
.explore-card p { font-size: .85rem; line-height: 1.55; color: var(--text-dim); }
.explore-card .formula-box { background: var(--surface2); border-radius: 6px; padding: 8px 12px; margin-top: 8px; font-family: var(--mono); font-size: .82rem; color: var(--gold); }
.explore-card .example-box { background: var(--surface2); border-radius: 6px; padding: 8px 12px; margin-top: 8px; font-size: .82rem; color: var(--text); }

/* ─── Practice ─── */
.practice-panel, .quiz-panel { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 16px; }
.practice-bar, .quiz-bar { display: flex; align-items: center; justify-content: space-between; margin-bottom: 14px; }
.practice-score { font-size: .88rem; color: var(--text-dim); }
.practice-score strong { color: var(--accent); }
.practice-prompt, .quiz-prompt { font-size: .95rem; line-height: 1.5; margin-bottom: 14px; }
.practice-input-row, .quiz-input-row { display: flex; align-items: center; gap: 8px; margin-bottom: 12px; }
.practice-input, .quiz-input { width: 120px; padding: 8px 10px; border-radius: 8px; border: 1px solid var(--border); background: var(--bg); color: var(--accent); font-family: var(--mono); font-size: .95rem; outline: none; }
.practice-input:focus, .quiz-input:focus { border-color: var(--accent); box-shadow: 0 0 0 2px var(--accent-lo); }
.practice-unit, .quiz-unit { font-size: .82rem; color: var(--text-dim); font-weight: 600; }
.practice-feedback, .quiz-feedback { font-size: .85rem; line-height: 1.5; margin-top: 8px; min-height: 20px; }

/* MCQ options */
.mcq-option { display: block; width: 100%; text-align: left; padding: 10px 14px; margin-bottom: 6px; border: 1px solid var(--border); border-radius: 8px; background: var(--bg); color: var(--text); font-size: .88rem; cursor: pointer; transition: all .15s; }
.mcq-option:hover { border-color: var(--accent); background: var(--accent-lo); }
.mcq-option.selected { border-color: var(--accent); background: var(--accent-lo); }
.mcq-option.correct { border-color: var(--green); background: rgba(61,220,132,.15); color: var(--green); }
.mcq-option.wrong { border-color: var(--red); background: rgba(255,85,85,.15); color: var(--red); }
.mcq-option:disabled { cursor: default; opacity: .7; }

/* Quiz result */
.quiz-result-row { padding: 10px 14px; border-radius: 8px; margin-bottom: 8px; font-size: .85rem; }
.quiz-result-row.correct { border-left: 3px solid var(--green); background: rgba(61,220,132,.08); }
.quiz-result-row.wrong { border-left: 3px solid var(--red); background: rgba(255,85,85,.08); }
.quiz-result-row .qr-q { color: var(--text); margin-bottom: 4px; }
.quiz-result-row .qr-a { color: var(--text-dim); font-size: .8rem; }
.quiz-stars { font-size: 1.6rem; text-align: center; margin: 12px 0; }
.quiz-score-display { text-align: center; font-size: 1.1rem; color: var(--accent); font-weight: 700; margin-bottom: 8px; }

/* Quiz actions */
.quiz-actions { display: flex; gap: 8px; margin-bottom: 12px; }

/* ─── User guide ─── */
.user-guide { margin-top: 30px; }
.user-guide h2 { font-size: 1.15rem; color: var(--accent); margin-bottom: 12px; }
.user-guide details { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; margin-bottom: 8px; }
.user-guide summary { padding: 12px 16px; cursor: pointer; font-weight: 600; font-size: .88rem; color: var(--text); list-style: none; display: flex; align-items: center; gap: 10px; }
.user-guide summary::-webkit-details-marker { display: none; }
.user-guide details[open] summary { border-bottom: 1px solid var(--border); }
.user-guide details > p, .user-guide details > ul { padding: 12px 16px; font-size: .85rem; line-height: 1.6; color: var(--text-dim); }
.user-guide ul { padding-left: 32px; }
.guide-section-num { display: inline-flex; align-items: center; justify-content: center; width: 22px; height: 22px; border-radius: 50%; background: var(--accent-lo); color: var(--accent); font-size: .72rem; font-weight: 700; flex-shrink: 0; }

/* ─── SEO article ─── */
.seo-article { margin-top: 40px; padding: 24px; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); }
.seo-article h2 { font-size: 1.15rem; color: var(--accent); margin-bottom: 14px; }
.seo-article h3 { font-size: .95rem; color: var(--text); margin: 16px 0 6px; }
.seo-article p { font-size: .85rem; line-height: 1.65; color: var(--text-dim); margin-bottom: 10px; }
.seo-article a { color: var(--accent); text-decoration: none; }
.seo-article a:hover { text-decoration: underline; }

/* ─── Responsive ─── */
@media (max-width: 768px) {
  h1 { font-size: 1.4rem; }
  .sim-slider-label { min-width: 80px; font-size: .78rem; }
  .stepper { min-width: 140px; }
  .info-row { grid-template-columns: repeat(3, 1fr); }
  .readout-badges { gap: 6px; }
}
@media (max-width: 500px) {
  #app { padding: 10px 12px 40px; }
  h1 { font-size: 1.15rem; }
  .controls-bar { gap: 6px; }
  .pill { padding: 5px 10px; font-size: .75rem; }
  .slider-row { flex-wrap: wrap; }
  .sim-slider-label { min-width: 100%; font-size: .78rem; }
  .stepper { min-width: 100%; }
  .info-row { grid-template-columns: 1fr 1fr; }
  .action-bar { flex-direction: column; }
  .readout-badge { padding: 4px 10px; font-size: .72rem; }
}