:root{
  --navy:#1a2238;
  --card:#0f1117;
  --ink:#e5e7eb;
  --muted:#a1a1aa;
  --btn:#e5e7eb;
  --btn-ink:#1a2238;
  --grid:#111827;
  --cell:#0b1326;
  --radius:16px;
  --shadow:0 1px 2px rgba(0,0,0,.12), 0 12px 36px rgba(0,0,0,.35);
  --gap:10px;
  --tile:#e5e7eb;
}

*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  background: var(--navy);
  color: var(--ink);
  font: 16px/1.6 system-ui, -apple-system, Segoe UI, Roboto, Inter, Arial, sans-serif;
}

.wrap{max-width:960px; margin:0 auto; padding:24px;}
.head h1{ margin:0; font-size: clamp(24px,4vw,40px); line-height:1.1; }
.tag{ margin:6px 0 12px; color: var(--muted); }

.hud{ display:flex; gap:12px; align-items:center; flex-wrap:wrap; }
.pill{
  background: rgba(255,255,255,0.06);
  border: 1px solid rgba(255,255,255,0.12);
  padding: 6px 10px;
  border-radius: 12px;
}
.nav{ display:flex; gap:10px; margin:10px 0 12px; }

.btn{
  display:inline-flex; align-items:center; gap:6px;
  padding:8px 12px;
  background: var(--btn);
  color: var(--btn-ink);
  border-radius:12px;
  border:1px solid rgba(255,255,255,0.6);
  text-decoration:none;
  font-weight:700;
  box-shadow: var(--shadow);
  cursor:pointer;
}
.btn:hover{ filter:brightness(0.96); }

.stage{
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  border:1px solid rgba(255,255,255,0.08);
  padding:16px;
  display:grid; 
  place-items:center;
  position: relative; /* keeps overlay contained */
}

/* Board */
.board{
  width: min(92vw, 440px);
  aspect-ratio: 1 / 1;
  background: var(--grid);
  border-radius: 14px;
  padding: var(--gap);
  display:grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: var(--gap);
  position: relative;
}

/* Tiles */
.tile{
  display:grid; place-items:center;
  border-radius: 10px;
  font-weight: 800;
  font-size: clamp(18px, 6vw, 36px);
  color: var(--tile);
  transition: transform .08s ease, background .12s ease, color .12s ease;
  user-select: none;
}
.tile.new{ animation: pop .12s ease-out; }
@keyframes pop{
  0%{ transform: scale(.6); opacity: .5; }
  100%{ transform: scale(1); opacity: 1; }
}

/* Color mapping */
.tile.v2    { background:#111827; color:#e5e7eb; }
.tile.v4    { background:#1f2937; color:#e5e7eb; }
.tile.v8    { background:#374151; color:#fff; }
.tile.v16   { background:#4b5563; color:#fff; }
.tile.v32   { background:#6b7280; color:#fff; }
.tile.v64   { background:#818cf8; color:#0b1020; }
.tile.v128  { background:#60a5fa; color:#0b1020; }
.tile.v256  { background:#34d399; color:#0b1020; }
.tile.v512  { background:#fbbf24; color:#0b1020; }
.tile.v1024 { background:#fb923c; color:#0b1020; }
.tile.v2048 { background:#f43f5e; color:#0b1020; }

/* Overlay */
.overlay{
  position:absolute;
  inset:0;
  display:none; /* hidden by default */
  place-items:center;
  background: rgba(0,0,0,0.45);
  color:#fff;
  border-radius: 14px;
  text-align:center;
  font-weight:800;
  font-size: 28px;
  text-shadow: 0 2px 8px rgba(0,0,0,.6);
}
.overlay.show { display:grid; } /* show only when active */

.hint{ color: var(--muted); margin-top: 10px; text-align:center; }