:root {
  --bg-a: #111625;
  --bg-b: #201637;
  --panel: rgba(12, 14, 32, 0.8);
  --border: rgba(151, 188, 224, 0.33);
  --text: #f2f7ff;
  --muted: #a6bad0;
  --accent: #ffbd5f;
  --accent-2: #70dbc8;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  color: var(--text);
  font-family: "Space Grotesk", "Trebuchet MS", sans-serif;
  background:
    radial-gradient(circle at 18% 11%, rgba(42, 139, 171, 0.24), transparent 34%),
    radial-gradient(circle at 83% 86%, rgba(233, 146, 73, 0.2), transparent 38%),
    linear-gradient(145deg, var(--bg-a), var(--bg-b));
}

.cubes-page {
  width: min(900px, 94vw);
  margin: 0 auto;
  padding: 1.2rem 0 2rem;
}

.topbar,
.hud,
.status-wrap,
.mode-wrap,
.board-wrap,
.controls {
  border: 1px solid var(--border);
  border-radius: 1rem;
  background: var(--panel);
}

.topbar {
  padding: 1rem;
}

.back-link {
  color: var(--accent-2);
  text-decoration: none;
}

.back-link:hover,
.back-link:focus-visible {
  text-decoration: underline;
}

.topbar h1 {
  margin: 0.4rem 0 0;
  font-size: clamp(1.9rem, 5vw, 2.8rem);
  font-family: "Fraunces", Georgia, serif;
}

.topbar p {
  margin: 0.45rem 0 0;
  color: var(--muted);
  max-width: 56ch;
}

.hud {
  margin-top: 0.8rem;
  padding: 0.82rem;
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.62rem;
}

.stat-card {
  border: 1px solid rgba(152, 188, 220, 0.24);
  border-radius: 0.8rem;
  padding: 0.6rem 0.72rem;
  display: grid;
  gap: 0.16rem;
  background: rgba(16, 24, 44, 0.6);
}

.label {
  text-transform: uppercase;
  font-size: 0.72rem;
  letter-spacing: 0.06em;
  color: var(--muted);
}

.stat-card strong {
  font-size: 1.34rem;
}

.next-card strong {
  color: var(--accent);
}

.status-wrap {
  margin-top: 0.8rem;
  padding: 0.75rem 0.9rem;
}

.status-wrap p {
  margin: 0;
  color: #d9e8f6;
}

.mode-wrap {
  margin-top: 0.8rem;
  padding: 0.7rem 0.9rem;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.mode-wrap label {
  color: var(--muted);
  font-size: 0.9rem;
}

.mode-wrap select {
  border: 0;
  border-radius: 0.6rem;
  font: inherit;
  background: #22384c;
  color: var(--text);
  padding: 0.5rem 0.62rem;
}

.board-wrap {
  margin-top: 0.8rem;
  padding: 1rem;
  display: grid;
  place-items: center;
}

.board {
  width: min(440px, 92vw);
  aspect-ratio: 1 / 2;
  border-radius: 0.9rem;
  background:
    linear-gradient(180deg, rgba(18, 22, 42, 0.96), rgba(12, 16, 32, 0.96)),
    radial-gradient(circle at 50% 0%, rgba(114, 203, 232, 0.16), transparent 50%);
  border: 1px solid rgba(155, 194, 225, 0.26);
  overflow: hidden;
}

.board--grid {
  padding: 0.45rem;
  display: grid;
  grid-template-columns: repeat(6, minmax(0, 1fr));
  grid-template-rows: repeat(12, minmax(0, 1fr));
  gap: 0.3rem;
}

.board--physics {
  padding: 0;
  position: relative;
  display: block;
}

.cube-cell {
  border-radius: 0.55rem;
  border: 1px solid rgba(122, 149, 174, 0.22);
  background: rgba(27, 34, 56, 0.78);
  display: grid;
  place-items: center;
  font-weight: 700;
  font-size: clamp(0.9rem, 2.7vw, 1.2rem);
  color: #f5fbff;
  text-shadow: 0 2px 5px rgba(0, 0, 0, 0.25);
}

.cube-cell.filled {
  border-color: rgba(255, 255, 255, 0.2);
  box-shadow: 0 7px 14px rgba(0, 0, 0, 0.26);
}

.cube-cell.active {
  outline: 2px solid rgba(255, 226, 156, 0.85);
  outline-offset: -2px;
}

.physics-cube {
  position: absolute;
  left: 0;
  top: 0;
  border-radius: 0.55rem;
  border: 1px solid rgba(122, 149, 174, 0.22);
  background: rgba(27, 34, 56, 0.78);
  display: grid;
  place-items: center;
  font-weight: 700;
  color: #f5fbff;
  text-shadow: 0 2px 5px rgba(0, 0, 0, 0.25);
  box-shadow: 0 7px 14px rgba(0, 0, 0, 0.26);
  will-change: transform;
  transform-origin: 50% 50%;
}

.physics-cube.active {
  outline: 2px solid rgba(255, 226, 156, 0.85);
  outline-offset: -2px;
}

.cube-cell[data-value="2"],
.physics-cube[data-value="2"] {
  background: linear-gradient(145deg, #ffd34d, #f5b200);
  color: #2b1d00;
}

.cube-cell[data-value="4"],
.physics-cube[data-value="4"] {
  background: linear-gradient(145deg, #32cc9f, #169f79);
}

.cube-cell[data-value="8"],
.physics-cube[data-value="8"] {
  background: linear-gradient(145deg, #ff5a7a, #e62f58);
}

.cube-cell[data-value="16"],
.physics-cube[data-value="16"] {
  background: linear-gradient(145deg, #38a8ff, #1b79d2);
}

.cube-cell[data-value="32"],
.physics-cube[data-value="32"] {
  background: linear-gradient(145deg, #ff9148, #e86b1a);
}

.cube-cell[data-value="64"],
.physics-cube[data-value="64"] {
  background: linear-gradient(145deg, #ac7dff, #8250ea);
}

.cube-cell[data-value="128"],
.physics-cube[data-value="128"] {
  background: linear-gradient(145deg, #f8f9fc, #dce6f8);
  color: #1b2b40;
}

.controls {
  margin-top: 0.8rem;
  padding: 0.8rem;
  display: grid;
  grid-template-columns: repeat(6, minmax(0, 1fr));
  gap: 0.6rem;
}

button {
  border: 0;
  border-radius: 0.65rem;
  padding: 0.62rem 0.74rem;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
  color: #08121f;
  background: linear-gradient(140deg, #ffd29a, #f9b169);
}

button.secondary {
  color: #e3eef8;
  background: linear-gradient(140deg, #30485d, #243747);
}

button:hover,
button:focus-visible {
  transform: translateY(-1px);
}

.hint {
  margin: 0.76rem 0 0;
  color: var(--muted);
  font-size: 0.92rem;
}

@media (max-width: 760px) {
  .hud {
    grid-template-columns: 1fr;
  }

  .controls {
    grid-template-columns: 1fr 1fr;
  }

  #start-btn,
  #new-game-btn {
    grid-column: span 2;
  }
}