* {
  box-sizing: border-box;
}

:root {
  --bg-top: #1a0e00;
  --bg-bottom: #080400;
  --panel: rgba(20, 10, 0, 0.78);
  --panel-border: rgba(245, 158, 11, 0.28);
  --text-main: #fef9f0;
  --text-dim: #c4a46b;
  --accent: #f59e0b;
  --accent-rgb: 245, 158, 11;
  --button-bg: linear-gradient(180deg, var(--accent), #d97706);
  --shadow: 0 18px 40px rgba(8, 3, 0, 0.34);
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at top, rgba(var(--accent-rgb), 0.12), transparent 34%),
    linear-gradient(180deg, var(--bg-top) 0%, var(--bg-bottom) 100%);
  color: var(--text-main);
  font-family: "Trebuchet MS", "Segoe UI", sans-serif;
}

.game-shell {
  width: min(100vw, 480px);
  min-height: 100vh;
  margin: 0 auto;
  padding: 12px;
  display: grid;
  grid-template-rows: auto minmax(0, 1fr);
  gap: 8px;
}

.topbar,
.playfield {
  border: 1px solid var(--panel-border);
  border-radius: 18px;
  background: var(--panel);
  box-shadow: var(--shadow);
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 12px;
}

.topbar-copy {
  display: grid;
  gap: 2px;
}

.eyebrow,
.label {
  color: var(--text-dim);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.title {
  font-size: 22px;
  line-height: 1;
}

#restart {
  border: 1px solid var(--accent);
  border-radius: 14px;
  background: var(--button-bg);
  color: #fff7ed;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.18);
  font: inherit;
  font-weight: 700;
  cursor: pointer;
  padding: 10px 14px;
  white-space: nowrap;
}

#restart:hover,
#restart:focus-visible {
  filter: brightness(1.08);
}

.playfield {
  min-height: 0;
  padding: 10px;
  display: grid;
  grid-template-rows: auto minmax(0, 1fr);
  gap: 8px;
}

.hud {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 6px;
  align-items: stretch;
}

.stat-card,
.status-wrap {
  border: 1px solid var(--panel-border);
  border-radius: 14px;
  background: rgba(25, 12, 0, 0.9);
  min-height: 0;
  display: grid;
  gap: 2px;
  align-content: center;
  padding: 8px 10px;
}

.status-wrap {
  grid-column: 1 / -1;
  background: linear-gradient(180deg, rgba(25, 12, 0, 0.96), rgba(12, 5, 0, 0.96));
}

.status-wrap[data-tone="win"] {
  border-color: var(--accent);
  box-shadow: inset 0 0 0 1px rgba(var(--accent-rgb), 0.16);
}

.status-wrap[data-tone="loss"] {
  border-color: #fb7185;
  box-shadow: inset 0 0 0 1px rgba(251, 113, 133, 0.16);
}

.hud strong {
  font-size: 18px;
  line-height: 1.1;
}

#status {
  font-size: 16px;
  line-height: 1.25;
}

.board-wrap {
  min-height: 0;
  display: grid;
  align-items: center;
  justify-items: center;
  overflow: hidden;
}

.grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  width: 100%;
  aspect-ratio: 1 / 1;
  background: rgba(10, 5, 0, 0.85);
  border: 1px solid rgba(var(--accent-rgb), 0.35);
  border-radius: 16px;
  padding: 8px;
  touch-action: none;
  box-shadow:
    inset 0 0 0 1px rgba(var(--accent-rgb), 0.06),
    0 0 18px rgba(var(--accent-rgb), 0.1);
}

.cell {
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: clamp(16px, 4.5vw, 26px);
  background: rgba(30, 15, 0, 0.6);
  color: var(--text-main);
  aspect-ratio: 1 / 1;
  min-height: 0;
}

.cell[data-value="2"]    { background: #3d2a0a; color: #fef9f0; }
.cell[data-value="4"]    { background: #5c3d0d; color: #fef9f0; }
.cell[data-value="8"]    { background: #92400e; color: #fff; }
.cell[data-value="16"]   { background: #b45309; color: #fff; }
.cell[data-value="32"]   { background: #d97706; color: #fff; }
.cell[data-value="64"]   { background: #f59e0b; color: #1a0a00; }
.cell[data-value="128"]  { background: #fbbf24; color: #1a0a00; font-size: clamp(14px, 3.8vw, 22px); }
.cell[data-value="256"]  { background: #fcd34d; color: #1a0a00; font-size: clamp(14px, 3.8vw, 22px); }
.cell[data-value="512"]  { background: #fde68a; color: #1a0a00; font-size: clamp(14px, 3.8vw, 22px); }
.cell[data-value="1024"] { background: #fef3c7; color: #1a0a00; font-size: clamp(11px, 3vw, 17px); }
.cell[data-value="2048"] {
  background: #fffbeb;
  color: #1a0a00;
  font-size: clamp(11px, 3vw, 17px);
  box-shadow: 0 0 20px rgba(245, 158, 11, 0.5);
}

@keyframes tile-pop {
  0%   { transform: scale(0); }
  60%  { transform: scale(1.1); }
  100% { transform: scale(1); }
}

@keyframes tile-merge {
  0%   { transform: scale(1); }
  50%  { transform: scale(1.15); }
  100% { transform: scale(1); }
}

.tile-new    { animation: tile-pop   0.15s ease; animation-fill-mode: none; }
.tile-merged { animation: tile-merge 0.2s  ease; animation-fill-mode: none; }

.cell[data-value="4096"],
.cell[data-value="8192"],
.cell[data-value="16384"],
.cell[data-value]:not([data-value=""]):not([data-value="2"]):not([data-value="4"]):not([data-value="8"]):not([data-value="16"]):not([data-value="32"]):not([data-value="64"]):not([data-value="128"]):not([data-value="256"]):not([data-value="512"]):not([data-value="1024"]):not([data-value="2048"]):not([data-value="4096"]):not([data-value="8192"]):not([data-value="16384"]) {
  background: #fff;
  color: #1a0a00;
  font-size: clamp(9px, 2.5vw, 14px);
  box-shadow: 0 0 28px rgba(245, 158, 11, 0.7);
}

/* ── Utilities ──────────────────────────────────────────────────────── */

.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;
}

/* ── Guide overlay ─────────────────────────────────────────────────── */

#guide-help {
  border: 1px solid var(--accent);
  border-radius: 14px;
  background: var(--button-bg);
  color: #fff7ed;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.18);
  font: inherit;
  font-weight: 700;
  cursor: pointer;
  padding: 8px 12px;
  white-space: nowrap;
}

#guide-help:hover,
#guide-help:focus-visible {
  filter: brightness(1.08);
}

.guide-overlay {
  position: fixed;
  inset: 0;
  z-index: 100;
  background: rgba(0, 0, 0, 0.72);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 16px;
  touch-action: none;
}

.guide-overlay[hidden] {
  display: none;
}

.guide-card {
  width: min(92vw, 380px);
  max-height: calc(100dvh - 32px);
  overflow-y: auto;
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 20px;
  padding: 28px 24px 20px;
  position: relative;
  box-shadow: 0 24px 56px rgba(0, 0, 0, 0.6);
}

.guide-close {
  position: absolute;
  top: 12px;
  right: 14px;
  background: none;
  border: none;
  color: var(--text-dim);
  font: inherit;
  font-size: 13px;
  cursor: pointer;
  padding: 4px 6px;
  border-radius: 8px;
}

.guide-close:hover,
.guide-close:focus-visible {
  color: var(--text-main);
  background: rgba(255, 255, 255, 0.08);
}

.guide-icon {
  font-size: 3rem;
  text-align: center;
  margin-bottom: 4px;
  line-height: 1;
}

.guide-arrows {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  grid-template-rows: 1fr 1fr;
  gap: 2px;
  width: 108px;
  margin: 0 auto 4px;
  font-size: 1.8rem;
}

.guide-arrows span {
  text-align: center;
  line-height: 1;
}

.guide-merge-demo {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  margin-bottom: 4px;
}

.guide-tile {
  width: 48px;
  height: 48px;
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 18px;
  color: var(--text-main);
}

.guide-tile[data-v="2"] { background: #3d2a0a; }
.guide-tile[data-v="4"] { background: #5c3d0d; }

.guide-plus {
  font-size: 20px;
  color: var(--text-dim);
  font-weight: 700;
}

.guide-title {
  font-size: 20px;
  margin: 10px 0 6px;
  text-align: center;
  color: var(--text-main);
}

.guide-body {
  font-size: 14px;
  color: var(--text-dim);
  line-height: 1.6;
  text-align: center;
  margin: 0;
}

.guide-body strong {
  color: var(--text-main);
}

.guide-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 22px;
  gap: 8px;
}

.guide-dots {
  display: flex;
  gap: 6px;
  align-items: center;
}

.guide-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: rgba(245, 158, 11, 0.25);
  transition: background 0.15s;
}

.guide-dot.active {
  background: var(--accent);
}

.guide-nav {
  display: flex;
  gap: 8px;
  align-items: center;
}

#guide-prev {
  background: none;
  border: 1px solid var(--panel-border);
  border-radius: 12px;
  color: var(--text-dim);
  font: inherit;
  font-size: 13px;
  cursor: pointer;
  padding: 8px 14px;
}

#guide-prev:hover,
#guide-prev:focus-visible {
  color: var(--text-main);
  border-color: var(--accent);
}

#guide-next {
  border: 1px solid var(--accent);
  border-radius: 12px;
  background: var(--button-bg);
  color: #fff7ed;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.18);
  font: inherit;
  font-weight: 700;
  cursor: pointer;
  padding: 8px 18px;
  white-space: nowrap;
}

#guide-next:hover,
#guide-next:focus-visible {
  filter: brightness(1.08);
}

/* ── Responsive ─────────────────────────────────────────────────────── */

@media (max-width: 520px) {
  body {
    min-height: 100svh;
    overflow: hidden;
  }

  .game-shell {
    height: 100svh;
    min-height: 0;
    padding: 6px 8px 8px;
    gap: 6px;
    overflow: hidden;
  }

  .topbar,
  .playfield {
    border-radius: 16px;
  }

  .topbar {
    padding: 6px 10px;
  }

  .title {
    font-size: 19px;
  }

  #restart,
  #guide-help {
    padding: 7px 11px;
  }

  .guide-card {
    padding: 22px 16px 16px;
  }

  .guide-title {
    font-size: 18px;
  }

  .guide-body {
    font-size: 13px;
  }

  .playfield {
    padding: 7px;
    gap: 6px;
  }

  .hud {
    gap: 4px;
  }

  .stat-card,
  .status-wrap {
    border-radius: 12px;
    padding: 5px 8px;
  }

  .hud strong {
    font-size: 16px;
  }

  #status {
    font-size: 14px;
  }

  .grid {
    gap: 6px;
    padding: 6px;
  }

  .cell {
    border-radius: 6px;
    font-size: clamp(14px, 4vw, 22px);
  }

  .cell[data-value="128"],
  .cell[data-value="256"],
  .cell[data-value="512"] {
    font-size: clamp(12px, 3.2vw, 18px);
  }

  .cell[data-value="1024"],
  .cell[data-value="2048"] {
    font-size: clamp(10px, 2.8vw, 15px);
  }

  .cell[data-value="4096"],
  .cell[data-value="8192"],
  .cell[data-value="16384"],
  .cell[data-value]:not([data-value=""]):not([data-value="2"]):not([data-value="4"]):not([data-value="8"]):not([data-value="16"]):not([data-value="32"]):not([data-value="64"]):not([data-value="128"]):not([data-value="256"]):not([data-value="512"]):not([data-value="1024"]):not([data-value="2048"]):not([data-value="4096"]):not([data-value="8192"]):not([data-value="16384"]) {
    font-size: clamp(8px, 2.2vw, 12px);
  }
}