:root {
  --bg: #faf8ef;
  --fg: #2b2b2b;
  --muted: #8f8a81;
  --board: #bbada0;
  --grid: #cdc1b4;
  --gap: 12px;
  --radius: 12px;
  --tile-radius: 10px;
  --title-size: 44px;
  --tile-size: 92px;
  --shadow: 0 8px 24px rgba(0, 0, 0, 0.08);
}

@media (max-width: 480px) {
  :root {
    --title-size: 36px;
    --tile-size: 70px;
    --gap: 10px;
  }
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1115;
    --fg: #f1f2f4;
    --muted: #a0a6b0;
    --board: #1b1e24;
    --grid: #2a2f38;
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
  }
}

* { box-sizing: border-box; }

html, body { height: 100%; }

body {
  margin: 0;
  font-family: "Noto Sans TC", system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "PingFang TC", "Microsoft JhengHei", "Noto Sans", sans-serif;
  color: var(--fg);
  background: radial-gradient(1200px 800px at 10% -10%, #ffffff70, transparent 50%), var(--bg);
}

.page {
  max-width: 720px;
  margin: 0 auto;
  padding: 28px 20px 40px;
}

.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.title {
  margin: 0;
  font-size: var(--title-size);
  font-weight: 800;
  letter-spacing: 1px;
}

.scores {
  display: flex;
  gap: 10px;
}

.score-block {
  background: linear-gradient(180deg, #f6f2e6, #ece3cc);
  color: #6b635b;
  min-width: 86px;
  padding: 8px 12px;
  border-radius: 10px;
  text-align: center;
  box-shadow: var(--shadow);
}

@media (prefers-color-scheme: dark) {
  .score-block {
    background: linear-gradient(180deg, #242833, #1b1e24);
    color: #e7e8ea;
  }
}

.score-block .label {
  font-size: 12px;
  opacity: 0.8;
}

.score-block .value {
  font-size: 20px;
  font-weight: 700;
}

.controls {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-top: 16px;
}

.hint {
  color: var(--muted);
  font-size: 14px;
}

.btn {
  appearance: none;
  border: none;
  padding: 10px 14px;
  border-radius: 10px;
  font-weight: 700;
  cursor: pointer;
  transition: transform 0.08s ease, box-shadow 0.2s ease, background 0.2s ease;
}

.btn-primary {
  background: linear-gradient(180deg, #f7b733, #f79233);
  color: #fff;
  box-shadow: var(--shadow);
}

.btn-primary:hover { filter: brightness(1.02); }
.btn-primary:active { transform: translateY(1px); }

.game { margin-top: 16px; }

.board {
  position: relative;
  width: min(100%, 640px);
  aspect-ratio: 1 / 1;
  margin: 10px auto 18px;
  background: var(--board);
  border-radius: var(--radius);
  padding: var(--gap);
  box-shadow: var(--shadow);
  touch-action: none;
}

.grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: var(--gap);
  width: 100%;
  height: 100%;
}

.grid-cell {
  background: var(--grid);
  border-radius: var(--tile-radius);
}

.tiles {
  position: absolute;
  inset: var(--gap);
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: var(--gap);
  pointer-events: none;
}

.tile {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 28px;
  font-weight: 800;
  border-radius: var(--tile-radius);
  box-shadow: inset 0 -4px 0 rgba(0,0,0,0.06), var(--shadow);
  transition: transform 0.08s ease;
  user-select: none;
}

.tile--new { animation: pop 160ms ease-out; }

@keyframes pop {
  0% { transform: scale(0.6); opacity: 0; }
  100% { transform: scale(1); opacity: 1; }
}

/* 顏色：數值對應 */
.tile[data-value="2"]   { background: #eee4da; color: #776e65; }
.tile[data-value="4"]   { background: #ede0c8; color: #776e65; }
.tile[data-value="8"]   { background: #f2b179; color: #f9f6f2; }
.tile[data-value="16"]  { background: #f59563; color: #f9f6f2; }
.tile[data-value="32"]  { background: #f67c5f; color: #f9f6f2; }
.tile[data-value="64"]  { background: #f65e3b; color: #f9f6f2; }
.tile[data-value="128"] { background: #edcf72; color: #f9f6f2; font-size: 24px; }
.tile[data-value="256"] { background: #edcc61; color: #f9f6f2; font-size: 24px; }
.tile[data-value="512"] { background: #edc850; color: #f9f6f2; font-size: 24px; }
.tile[data-value="1024"]{ background: #edc53f; color: #f9f6f2; font-size: 22px; }
.tile[data-value="2048"]{ background: #edc22e; color: #f9f6f2; font-size: 22px; }
.tile[data-value="4096"],
.tile[data-value="8192"],
.tile[data-value="16384"],
.tile[data-value="32768"] {
  background: #3c3a32;
  color: #f9f6f2;
  font-size: 20px;
}

.footer { color: var(--muted); }

/* Overlay */
.overlay {
  position: fixed;
  inset: 0;
  display: grid;
  place-items: center;
  background: rgba(0,0,0,0.35);
  backdrop-filter: blur(2px);
  padding: 20px;
}

.overlay.hidden { display: none; }

.overlay-card {
  width: 100%;
  max-width: 360px;
  background: var(--bg);
  color: var(--fg);
  border-radius: 14px;
  padding: 18px 18px 16px;
  box-shadow: var(--shadow);
  text-align: center;
}

.overlay-title { margin: 0 0 8px; }
.overlay-text { margin: 0 0 14px; color: var(--muted); }
.overlay-actions { display: flex; justify-content: center; }

/* 無障礙用隱藏類別 */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.lang-select {
  padding: 8px 10px;
  border-radius: 10px;
  border: 1px solid rgba(0,0,0,0.08);
  background: #ffffff;
  color: var(--fg);
  font-weight: 700;
  box-shadow: var(--shadow);
}

@media (prefers-color-scheme: dark) {
  .lang-select {
    background: #1b1e24;
    border-color: rgba(255,255,255,0.08);
    color: #e7e8ea;
  }
}