:root {
  --bg: #0e1116;
  --bg2: #161b22;
  --card: #1c232d;
  --line: #2a323d;
  --text: #e6edf3;
  --muted: #9aa7b4;
  --accent: #4f8cff;
  --accent2: #2ea043;
  --radius: 14px;
}

* { box-sizing: border-box; }
html, body { margin: 0; height: 100%; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: radial-gradient(1200px 600px at 70% -10%, #1b2430, var(--bg));
  color: var(--text);
  min-height: 100%;
}

.top-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 24px;
  border-bottom: 1px solid var(--line);
  background: var(--bg2);
  width: 100%;
}
.top-bar-left {
  display: flex;
  align-items: center;
}
.top-bar-title {
  font-size: 20px;
  font-weight: 600;
  color: var(--text);
  margin: 0;
}
.top-bar-right {
  display: flex;
  align-items: center;
  gap: 16px;
}
.top-bar-link {
  font-size: 14px;
  color: var(--muted);
  text-decoration: none;
  font-weight: 500;
  transition: color 0.15s;
  display: flex;
  align-items: center;
  gap: 4px;
}
.top-bar-link:hover {
  color: var(--accent);
}
.top-bar-donate {
  font-size: 14px;
  font-weight: 600;
  color: #fff;
  background: linear-gradient(135deg, #ff4d4f, #c3002f);
  padding: 6px 14px;
  border-radius: 999px;
  text-decoration: none;
  transition: filter 0.15s;
}
.top-bar-donate:hover {
  filter: brightness(0.9);
}
.tagline { margin: 4px 0 0; color: var(--muted); font-size: 14px; }
.tagline-container {
  padding: 16px 24px 0;
  margin: 0;
}

.layout {
  display: grid;
  grid-template-columns: 1fr 380px;
  gap: 20px;
  padding: 16px 24px 40px;
  align-items: start;
}
@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; }
  .top-bar {
    padding: 12px 16px;
  }
  .top-bar-title {
    font-size: 18px;
  }
  .top-bar-link, .top-bar-donate {
    font-size: 13px;
  }
  .tagline-container {
    padding: 12px 16px 0;
  }
}

/* Khối 3D */
.stage {
  background: linear-gradient(180deg, #11161d, #0c1015);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  position: sticky;
  top: 16px;
}
.cube3d {
  width: 100%;
  height: 480px;
  touch-action: none;
  cursor: grab;
}
.cube3d:active { cursor: grabbing; }
.stage-hint {
  padding: 10px 14px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 13px;
  text-align: center;
}

/* Panel */
.panel { display: flex; flex-direction: column; gap: 16px; }
.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px;
}
.card h2 { margin: 0 0 6px; font-size: 15px; letter-spacing: .3px; }
.muted { color: var(--muted); font-size: 13px; margin: 4px 0 12px; }
.hidden { display: none !important; }

/* Palette */
.palette {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 8px;
  margin-bottom: 14px;
}
.swatch {
  aspect-ratio: 1;
  border-radius: 10px;
  border: 3px solid transparent;
  cursor: pointer;
  position: relative;
  transition: transform .08s;
}
.swatch:hover { transform: translateY(-2px); }
.swatch.active { border-color: var(--text); box-shadow: 0 0 0 2px var(--accent); }

/* Buttons */
.btn {
  border: 1px solid var(--line);
  background: var(--bg2);
  color: var(--text);
  padding: 9px 12px;
  border-radius: 10px;
  cursor: pointer;
  font-size: 13px;
  transition: background .12s, border-color .12s;
}
.btn:hover { border-color: var(--accent); }
.btn.ghost { background: transparent; }
.btn.small { padding: 6px 10px; font-size: 12px; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; font-weight: 600; }
.btn.primary:hover { filter: brightness(1.08); }
.btn.big { width: 100%; padding: 13px; font-size: 15px; margin-top: 14px; }
.btn-row { display: flex; gap: 8px; }
.btn-row .btn { flex: 1; }

/* Method */
.method { display: flex; flex-direction: column; gap: 8px; }
.radio {
  display: flex; align-items: center; gap: 10px;
  border: 1px solid var(--line); border-radius: 10px;
  padding: 10px 12px; cursor: pointer;
}
.radio:has(input:checked) { border-color: var(--accent); background: #1a2535; }
.radio span { display: flex; flex-direction: column; }
.radio small { color: var(--muted); font-size: 12px; }
.radio input { accent-color: var(--accent); }

.msg { margin-top: 12px; font-size: 13px; min-height: 18px; }
.msg.err { color: #ff7b72; }
.msg.ok { color: #56d364; }
.msg.info { color: var(--accent); }

/* Player */
.play-head { display: flex; justify-content: space-between; align-items: center; }
.player { margin: 14px 0; text-align: center; }
.counter { font-size: 28px; font-weight: 700; font-variant-numeric: tabular-nums; }
.stage-label { color: var(--accent); font-size: 14px; min-height: 20px; margin: 4px 0 12px; }
.controls { display: flex; justify-content: center; gap: 8px; margin-bottom: 14px; }
.ctrl {
  width: 46px; height: 46px; border-radius: 12px;
  border: 1px solid var(--line); background: var(--bg2); color: var(--text);
  font-size: 16px; cursor: pointer;
}
.ctrl:hover { border-color: var(--accent); }
.ctrl.play { background: var(--accent2); border-color: var(--accent2); color: #fff; width: 56px; }
.speed { display: flex; align-items: center; gap: 10px; justify-content: center; font-size: 13px; color: var(--muted); }
.speed input { accent-color: var(--accent); }

.moves-title { font-size: 13px; color: var(--muted); margin: 8px 0; }
.moves { display: flex; flex-wrap: wrap; gap: 6px; max-height: 260px; overflow-y: auto; }
.stage-group { width: 100%; }
.stage-group .gname {
  font-size: 12px; color: var(--accent); margin: 8px 0 6px; font-weight: 600;
}
.stage-group .chips { display: flex; flex-wrap: wrap; gap: 6px; }
.chip {
  font-family: ui-monospace, "SF Mono", Menlo, monospace;
  font-size: 13px; font-weight: 600;
  padding: 5px 9px; border-radius: 8px;
  background: var(--bg2); border: 1px solid var(--line);
  min-width: 30px; text-align: center;
}
.chip.done { opacity: .45; }
.chip.current { background: var(--accent); border-color: var(--accent); color: #fff; transform: scale(1.08); }