:root {
  color-scheme: dark;
  --bg: #faf8ef;
  --panel: #fbf7ef;
  --text: #776e65;
  --muted: #8f7a66;
  --accent: #edc22e;
  --accent-2: #f2b179;
  --tile-empty: #cdc1b4;
  --tile-border: #bbada0;
  --shadow: 0 8px 20px rgba(60, 50, 40, 0.12);
  --board-bg: #bbada0;
  --score-bg: #eee4da;
  --score-text: #776e65;
  --btn-bg: #8f7a66;
  --btn-text: #ffffff;
  --btn-shadow: inset 0 -2px 0 rgba(0, 0, 0, 0.15);
  --tile-0-bg: rgba(238, 228, 218, 0.35);
  --tile-2-bg: #eee4da;
  --tile-2-text: #776e65;
  --tile-4-bg: #ede0c8;
  --tile-4-text: #776e65;
  --tile-8-bg: #f2b179;
  --tile-8-text: #ffffff;
  --tile-16-bg: #f59563;
  --tile-16-text: #ffffff;
  --tile-32-bg: #f67c5f;
  --tile-32-text: #ffffff;
  --tile-64-bg: #f65e3b;
  --tile-64-text: #ffffff;
  --tile-128-bg: #edcf72;
  --tile-128-text: #ffffff;
  --tile-256-bg: #edcc61;
  --tile-256-text: #ffffff;
  --tile-512-bg: #edc850;
  --tile-512-text: #ffffff;
  --tile-1024-bg: #edc53f;
  --tile-1024-text: #ffffff;
  --tile-2048-bg: #edc22e;
  --tile-2048-text: #ffffff;
}

html[data-theme='light'] {
  color-scheme: light;
  --bg: #faf8ef;
  --panel: #fbf7ef;
  --text: #776e65;
  --muted: #8f7a66;
  --accent: #edc22e;
  --accent-2: #f2b179;
  --tile-empty: #cdc1b4;
  --tile-border: #bbada0;
  --shadow: 0 8px 20px rgba(60, 50, 40, 0.12);
  --board-bg: #bbada0;
  --score-bg: #eee4da;
  --score-text: #776e65;
  --btn-bg: #8f7a66;
  --btn-text: #ffffff;
  --btn-shadow: inset 0 -2px 0 rgba(0, 0, 0, 0.15);
  --tile-0-bg: rgba(238, 228, 218, 0.35);
  --tile-2-bg: #eee4da;
  --tile-2-text: #776e65;
  --tile-4-bg: #ede0c8;
  --tile-4-text: #776e65;
  --tile-8-bg: #f2b179;
  --tile-8-text: #ffffff;
  --tile-16-bg: #f59563;
  --tile-16-text: #ffffff;
  --tile-32-bg: #f67c5f;
  --tile-32-text: #ffffff;
  --tile-64-bg: #f65e3b;
  --tile-64-text: #ffffff;
  --tile-128-bg: #edcf72;
  --tile-128-text: #ffffff;
  --tile-256-bg: #edcc61;
  --tile-256-text: #ffffff;
  --tile-512-bg: #edc850;
  --tile-512-text: #ffffff;
  --tile-1024-bg: #edc53f;
  --tile-1024-text: #ffffff;
  --tile-2048-bg: #edc22e;
  --tile-2048-text: #ffffff;
}

html[data-theme='dark'] {
  color-scheme: dark;
  --bg: #0f172a;
  --panel: #111827;
  --text: #f3f4f6;
  --muted: #cbd5e1;
  --accent: #f59e0b;
  --accent-2: #f97316;
  --tile-empty: #334155;
  --tile-border: #475569;
  --shadow: 0 8px 20px rgba(0, 0, 0, 0.25);
  --board-bg: #1f2937;
  --score-bg: #1f2937;
  --score-text: #e5e7eb;
  --btn-bg: #334155;
  --btn-text: #f8fafc;
  --btn-shadow: inset 0 -2px 0 rgba(0, 0, 0, 0.3);
  --tile-0-bg: rgba(15, 23, 42, 0.6);
  --tile-2-bg: #334155;
  --tile-2-text: #f8fafc;
  --tile-4-bg: #475569;
  --tile-4-text: #f8fafc;
  --tile-8-bg: #7c3aed;
  --tile-8-text: #ffffff;
  --tile-16-bg: #8b5cf6;
  --tile-16-text: #ffffff;
  --tile-32-bg: #a78bfa;
  --tile-32-text: #111827;
  --tile-64-bg: #c084fc;
  --tile-64-text: #111827;
  --tile-128-bg: #f59e0b;
  --tile-128-text: #111827;
  --tile-256-bg: #f97316;
  --tile-256-text: #ffffff;
  --tile-512-bg: #fb923c;
  --tile-512-text: #111827;
  --tile-1024-bg: #facc15;
  --tile-1024-text: #111827;
  --tile-2048-bg: #fde68a;
  --tile-2048-text: #111827;
}

* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: "Clear Sans", "Segoe UI", Roboto, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
}

button { font: inherit; }

.game-shell {
  min-height: 100vh;
  display: grid;
  place-items: center;
  padding: 1rem;
}

.panel {
  width: min(560px, 100%);
  background: var(--panel);
  border-radius: 18px;
  box-shadow: var(--shadow);
  padding: 1rem;
}

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.8rem;
  margin-bottom: 0.9rem;
  flex-wrap: wrap;
}

h1 {
  margin: 0;
  font-size: clamp(1.6rem, 3vw, 2.1rem);
  font-weight: 700;
  letter-spacing: 0.02em;
}

.actions {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.btn {
  border: 0;
  border-radius: 10px;
  padding: 0.7rem 0.9rem;
  cursor: pointer;
  background: var(--btn-bg);
  color: var(--btn-text);
  min-height: 42px;
  line-height: 1;
  transition: transform 120ms ease, box-shadow 120ms ease;
  font-size: 0.95rem;
  box-shadow: var(--btn-shadow);
}

.btn:active {
  transform: scale(0.97);
}

.btn-primary {
  background: var(--btn-bg);
  color: var(--btn-text);
  border: 0;
}

.scores {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.6rem;
  margin-bottom: 0.8rem;
}

.score-card {
  background: var(--score-bg);
  border-radius: 10px;
  padding: 0.7rem 0.8rem;
  color: var(--score-text);
}

.score-card span {
  display: block;
  font-size: 0.8rem;
  color: var(--muted);
  margin-bottom: 0.2rem;
}

.score-card strong {
  font-size: 1.1rem;
}

.status {
  color: var(--muted);
  margin-bottom: 0.8rem;
  font-size: 0.95rem;
}

.board {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.6rem;
  background: var(--board-bg);
  border-radius: 14px;
  padding: 0.65rem;
  aspect-ratio: 1;
  touch-action: none;
  user-select: none;
  width: 100%;
}

.tile {
  border-radius: 10px;
  display: grid;
  place-items: center;
  font-weight: 700;
  font-size: clamp(0.9rem, 2vw, 1.25rem);
  min-height: 58px;
  background: var(--tile-empty);
  color: var(--text);
  border: 1px solid var(--tile-border);
  transition: transform 180ms cubic-bezier(.2,.8,.2,1), background 180ms ease;
  will-change: transform;
}

.board.is-animating .tile {
  animation: tile-slide 180ms cubic-bezier(.2,.8,.2,1);
}

.tile--0 { background: var(--tile-0-bg); color: transparent; border-color: transparent; }
.tile--2 { background: var(--tile-2-bg); color: var(--tile-2-text); }
.tile--4 { background: var(--tile-4-bg); color: var(--tile-4-text); }
.tile--8 { background: var(--tile-8-bg); color: var(--tile-8-text); }
.tile--16 { background: var(--tile-16-bg); color: var(--tile-16-text); }
.tile--32 { background: var(--tile-32-bg); color: var(--tile-32-text); }
.tile--64 { background: var(--tile-64-bg); color: var(--tile-64-text); }
.tile--128 { background: var(--tile-128-bg); color: var(--tile-128-text); }
.tile--256 { background: var(--tile-256-bg); color: var(--tile-256-text); }
.tile--512 { background: var(--tile-512-bg); color: var(--tile-512-text); }
.tile--1024 { background: var(--tile-1024-bg); color: var(--tile-1024-text); }
.tile--2048 { background: var(--tile-2048-bg); color: var(--tile-2048-text); }

@keyframes tile-slide {
  0% { transform: translateY(6px) scale(0.94); opacity: 0.85; }
  60% { transform: translateY(-1px) scale(1.02); }
  100% { transform: translateY(0) scale(1); opacity: 1; }
}

@media (max-width: 640px) {
  .game-shell { padding: 0.6rem; }
  .panel { padding: 0.8rem; border-radius: 18px; }
  .topbar { flex-direction: column; align-items: flex-start; }
  .actions { width: 100%; }
  .btn { flex: 1; text-align: center; border-radius: 13px; }
  .scores { gap: 0.45rem; }
  .board { gap: 0.5rem; padding: 0.55rem; }
  .tile { min-height: 54px; border-radius: 12px; }
}