:root {
  --bg: #faf8ef;
  --board-bg: #bbada0;
  --cell-bg: rgba(238, 228, 218, 0.35);
  --text: #3c3a32;
  --accent: #8f7a66;
  --accent2: #edc22e;
  --grad: linear-gradient(120deg, var(--accent), var(--accent2));
  --btn-c1: var(--accent);
  --btn-c2: var(--accent2);
  --btn-grad: linear-gradient(120deg, var(--btn-c1), var(--btn-c2));
  --card-bg: #ffffff;
  --card-border: #e8e0d3;
  --muted: #6b6355;
  --hero-grid: rgba(20, 20, 40, 0.05);
}

:root[data-theme="dark"] {
  --accent: #b39c86;
  --accent2: #f5d76e;
  /* ボタンの塗りは文字用のaccentよりトーンを落として、暗い背景で発光しすぎないようにする */
  --btn-c1: #8f7a66;
  --btn-c2: #edc22e;
  --bg: #121214;
  --text: #ececee;
  --card-bg: #1c1c20;
  --card-border: #2c2c31;
  --muted: #9a9aa2;
  --hero-grid: rgba(255, 255, 255, 0.06);
}
:root[data-theme="dark"] .ad-slot {
  background: repeating-linear-gradient(45deg, #1c1c20, #1c1c20 10px, #232328 10px, #232328 20px);
  color: var(--muted);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Hiragino Sans", "Yu Gothic", "Meiryo", sans-serif;
  background-color: var(--bg);
  background-image:
    radial-gradient(circle, var(--hero-grid) 1px, transparent 1px),
    radial-gradient(900px circle at 15% -10%, color-mix(in srgb, var(--accent) 12%, transparent), transparent 55%),
    radial-gradient(800px circle at 100% 10%, color-mix(in srgb, var(--accent2) 9%, transparent), transparent 55%);
  background-size: 22px 22px, auto, auto;
  background-attachment: fixed;
  color: var(--text);
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  align-items: center;
}

.site-header {
  text-align: center;
  padding: 1.2rem 1rem 0.4rem;
}

.site-header h1 {
  margin: 0;
  font-size: 1.8rem;
  font-weight: 800;
  letter-spacing: -0.01em;
  background: var(--grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.subtitle {
  margin: 0.3rem 0 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.ad-slot {
  width: 100%;
  max-width: 640px;
  min-height: 60px;
  margin: 0.8rem auto;
  display: flex;
  align-items: center;
  justify-content: center;
  background: repeating-linear-gradient(45deg, #eee, #eee 10px, #e2e2e2 10px, #e2e2e2 20px);
  color: var(--muted);
  font-size: 0.8rem;
  border-radius: 6px;
}

main {
  width: 100%;
  max-width: 480px;
  padding: 0 1rem 2rem;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.status-bar {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.8rem;
  gap: 0.5rem;
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  font-weight: bold;
  font-size: 1.2rem;
  background: var(--board-bg);
  color: #fff;
  padding: 0.3rem 0.8rem;
  border-radius: 6px;
  min-width: 70px;
}

.stat-label {
  font-size: 0.7rem;
  font-weight: normal;
  color: #eee4da;
}

.reset-btn {
  padding: 0.5rem 1rem;
  border: none;
  border-radius: 6px;
  background: var(--btn-grad);
  color: #fff;
  font-size: 0.9rem;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.reset-btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 16px color-mix(in srgb, var(--btn-c1) 35%, transparent);
}

.board-wrapper {
  width: 100%;
  display: flex;
  justify-content: center;
  touch-action: none;
}

.board {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: 0.6rem;
  background: var(--board-bg);
  border-radius: 8px;
  padding: 0.6rem;
  width: 100%;
  max-width: 420px;
  aspect-ratio: 1 / 1;
}

.cell {
  background: var(--cell-bg);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.6rem;
  font-weight: bold;
  color: var(--text);
  transition: background 0.1s;
}

.cell[data-value="2"] { background: #eee4da; }
.cell[data-value="4"] { background: #ede0c8; }
.cell[data-value="8"] { background: #f2b179; color: #fff; }
.cell[data-value="16"] { background: #f59563; color: #fff; }
.cell[data-value="32"] { background: #f67c5f; color: #fff; }
.cell[data-value="64"] { background: #f65e3b; color: #fff; }
.cell[data-value="128"] { background: #edcf72; color: #fff; font-size: 1.4rem; }
.cell[data-value="256"] { background: #edcc61; color: #fff; font-size: 1.4rem; }
.cell[data-value="512"] { background: #edc850; color: #fff; font-size: 1.4rem; }
.cell[data-value="1024"] { background: #edc53f; color: #fff; font-size: 1.2rem; }
.cell[data-value="2048"] { background: #edc22e; color: #fff; font-size: 1.2rem; }

.touch-controls {
  margin-top: 1rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.4rem;
}

.dir-row {
  display: flex;
  gap: 0.4rem;
}

.dir-btn {
  width: 48px;
  height: 48px;
  border-radius: 8px;
  border: none;
  background: var(--btn-grad);
  color: #fff;
  font-size: 1.1rem;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.dir-btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 16px color-mix(in srgb, var(--btn-c1) 35%, transparent);
}

.dir-btn:active {
  opacity: 0.8;
}

.overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.55);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
}

.overlay.hidden {
  display: none;
}

.overlay-card {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  padding: 1.5rem 2rem;
  text-align: center;
  max-width: 90%;
  width: 360px;
  position: relative;
  z-index: 1001;
}

.result-text {
  font-size: 1.4rem;
  font-weight: bold;
  margin: 0 0 0.5rem;
}

.result-detail {
  color: var(--muted);
  margin: 0 0 1rem;
}

.other-games {
  margin-top: 1.2rem;
  border-top: 1px solid var(--card-border);
  padding-top: 1rem;
}

.other-games p {
  margin: 0 0 0.5rem;
  font-weight: bold;
  color: var(--muted);
}

.other-games ul {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  justify-content: center;
}

.other-games a {
  display: inline-block;
  padding: 0.4rem 0.8rem;
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 999px;
  color: var(--accent);
  text-decoration: none;
  font-size: 0.85rem;
  transition: border-color 0.15s ease, transform 0.15s ease;
}

.other-games a:hover {
  border-color: var(--accent);
  transform: translateY(-1px);
}

.howto {
  width: 100%;
  margin-top: 2rem;
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  padding: 1rem 1.2rem;
  border-radius: 8px;
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.06);
}

.howto h2 {
  margin-top: 0;
  font-size: 1.2rem;
}

.howto ul {
  padding-left: 1.2rem;
  line-height: 1.6;
}

.site-footer {
  margin-top: auto;
  padding: 1rem;
  color: var(--muted);
  font-size: 0.8rem;
}

@media (max-width: 480px) {
  .site-header h1 {
    font-size: 1.4rem;
  }
  .cell {
    font-size: 1.2rem;
  }
  .overlay-card {
    padding: 1.2rem 1rem;
  }
}

.site-nav {
  width: 100%;
  padding: 0.6rem 1rem;
  font-size: 0.85rem;
  box-sizing: border-box;
}
.site-nav a {
  display: inline-flex;
  align-items: center;
  color: var(--text);
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 999px;
  padding: 0.35rem 0.9rem;
  text-decoration: none;
  transition: border-color 0.15s ease, transform 0.15s ease;
}
.site-nav a:hover {
  border-color: var(--accent);
  transform: translateY(-1px);
}